The system currently takes a csv file to be uploaded and populates the fields, after adding our partnership lookup field object below:


The upload has been displaying this error and failing:

processing started...
The following error has occurred.
FIELD_FILTER_VALIDATION_EXCEPTION: Account selected is not a partner. Account fields that affected this error:
(Partnership__c)
Row index : 552
The following error has occurred.
FIELD_FILTER_VALIDATION_EXCEPTION: Account selected is not a partner. Account fields that affected this error:
(Partnership__c)
Row index : 1082
The following error has occurred.
FIELD_FILTER_VALIDATION_EXCEPTION: Account selected is not a partner. Account fields that affected this error:
(Partnership__c)
Row index : 1122
.....

I have looked at the idea of perhaps the field filter being the issue but this doesn't appear to be the case, I have looked over my import class and seem to have hit a wall, if anyone can pin point where the issue seems to stem from that would be hugely appreciated. My apex class is below and hopefully you can give me some advice.

EnquixAccountImportBatch 

global without sharing class EnquixAccountImportBatch implements Database.Batchable<String>, Database.Stateful {

    @TestVisible private Enqix_Import__c currentRecord;
    @TestVisible private Boolean headerProcessed;
    @TestVisible private Integer startRow;
    @TestVisible private String csvFile;
    @TestVisible private List<String> messages;
    @TestVisible private Map<String, Integer> headerIndexes;

    global EnquixAccountImportBatch() {

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch .ctor - start');
        messages = new List<String>();

        headerProcessed = false;

        List<Enqix_Import__c> enqixImports = EquixImportManager.getPendingEnqixImports(EquixImportManager.IMPORT_TYPE_ACCOUNT);
        System.debug(LoggingLevel.DEBUG, 'enqixImports : ' + enqixImports);

        if (enqixImports.size() > 0) {

            currentRecord = enqixImports[0];
            currentRecord.Status__c = EquixImportManager.STATUS_IN_PROGRESS;
            update currentRecord;
        }

        System.debug(LoggingLevel.DEBUG, 'currentRecord: ' + currentRecord);
        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch .ctor - end');
    }

    global Iterable<String> start(Database.BatchableContext info) {

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch start - start');
        messages.add('processing started...');

        try {

            if (currentRecord == null) {

                System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch start - end no records');
                return new List<String>();
            }
            else {

                Attachment att = EquixImportManager.getLatestAttachmentForEnqixImport(currentRecord.Id);
//                csvFile = att.Body.toString();
//                if (!csvFile.endsWith(Parser.CRLF)) {
//
//                    csvFile += Parser.CRLF;
//                }
                //csvFile = csvFile.subString(csvFile.indexOf(Parser.CRLF) + Parser.CRLF.length(), csvFile.length());
                System.debug('Final heap size: ' +  Limits.getHeapSize());

                System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch start - end processing');

                return new CSVIterator(att.Body.toString(), Parser.CRLF);
            }
        }
        catch (Exception ex) {

            System.debug(LoggingLevel.ERROR, ex.getMessage() + ' :: ' + ex.getStackTraceString());
            System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch start - end no attachment');
            messages.add(String.format('Error while parsing Enquix Import: {0}. Error details: {1}. Stack Trace: {2}', new List<String> {
                    currentRecord.Id, ex.getMessage(), ex.getStackTraceString()
            })) ;
            return new List<String>();
        }
    }

    global void execute(Database.BatchableContext info, List<String> scope) {

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch execute - start');
        System.debug(LoggingLevel.DEBUG, 'scope.size(): ' + scope.size());
        //first create new csv from the scope lines
        String importFile = '';
        for (String row : scope) {

            importFile += row + Parser.CRLF;
        }

        List<List<String>> parsedData = new List<List<String>>();
        try {

            parsedData = CSVReader.readCSVFile(importFile);
        }
        catch (Exception ex) {

            messages.add(String.format('Error while parsing Enquix Import: {0}. Error details: {1}', new List<String> {
                    currentRecord.Id, ex.getStackTraceString()
            }));
            System.debug(LoggingLevel.ERROR, ex.getMessage() + '\n' + ex.getStackTraceString());

            return;
        }
        System.debug(LoggingLevel.DEBUG, 'parsedData.size(): ' + parsedData.size());
        //then process header if needed
        System.debug(LoggingLevel.DEBUG, 'headerProcessed: ' + headerProcessed);
        if (!headerProcessed) {

            headerIndexes = EquixImportManager.processHeader(parsedData[0]);
            headerProcessed = true;
            parsedData.remove(0);
        }

        List<Account> accounts = new List<Account>();
        Set<String> accountsEnqixIdSet = new Set<String>();

        for (List<String> csvLine : parsedData) {
            try{
                if (!accountsEnqixIdSet.contains(csvLine.get(headerIndexes.get(EnquixImportMappingsManager.PARENT_ID_LOCATION_MAPPING)))) {

                    accounts.add(AccountManager.createAccountRecordFromCSVLine(
                            csvLine
                            , EquixImportManager.getImportMappingMap().get(
                                    EquixImportManager.IMPORT_TYPE_ACCOUNT).get(
                                    EnquixImportMappingsManager.ACCOUNT_RECORD_GROUP)
                            , headerIndexes
                    ));

                    accountsEnqixIdSet.add(csvLine.get(headerIndexes.get(EnquixImportMappingsManager.PARENT_ID_LOCATION_MAPPING)));
                }
            }
            catch(Exception ex) {
                messages.add('The following error has occurred.\n' + ex.getStackTraceString() + ': ' + ex.getMessage() + '. Row causing the error:' + String.join(csvLine, ','));

                System.debug('The following error has occurred.');
                System.debug(ex.getStackTraceString() + ': ' + ex.getMessage());
                System.debug('Row causing the error:' + String.join(csvLine, ','));
            }


        }
        System.debug(LoggingLevel.DEBUG, 'accounts.size(): ' + accounts.size());

        Database.UpsertResult[] saveResults = Database.upsert(accounts, Account.Enqix_ID__c, false);
        Integer listIndex = 0; // We start at 2 because the CSV data starts in row 2

        for (Database.UpsertResult sr : saveResults) {
            if (!sr.isSuccess()) {
                for (Database.Error err : sr.getErrors()) {
                    messages.add('The following error has occurred.\n' + err.getStatusCode() + ': ' + err.getMessage() + '. Account fields that affected this error:\n ' + err.getFields() + '\NRow index : ' + listIndex+2);

                    System.debug('The following error has occurred.');
                    System.debug(err.getStatusCode() + ': ' + err.getMessage());
                    System.debug('Account fields that affected this error: ' + err.getFields());
                    System.debug('The error was caused by the sobject at index: ' + listIndex);
                    System.debug(accounts.get(listIndex));

                }
            }
            listIndex++;
        }

        List<Account> locations = new List<Account>();

        for (List<String> csvLine : parsedData) {

            locations.add(AccountManager.createLocationRecordFromCSVLine(
                    csvLine
                    , EquixImportManager.getImportMappingMap().get(
                            EquixImportManager.IMPORT_TYPE_ACCOUNT).get(
                            EnquixImportMappingsManager.LOCATION_RECORD_GROUP)
                    , headerIndexes
            ));
        }
        System.debug(LoggingLevel.DEBUG, 'locations.size(): ' + locations.size());

        saveResults = Database.upsert(locations, Account.Enqix_Location_ID__c, false);
        listIndex = 0; // We start at 2 because the CSV data starts in row 2

        for (Database.UpsertResult sr : saveResults) {
            if (!sr.isSuccess()) {
                for (Database.Error err : sr.getErrors()) {
                    messages.add('The following error has occurred.\n' + err.getStatusCode() + ': ' + err.getMessage() + '. Account fields that affected this error:\n ' + err.getFields() + '\NRow index : ' + listIndex+2);

                    System.debug('The following error has occurred.');
                    System.debug(err.getStatusCode() + ': ' + err.getMessage());
                    System.debug('Account fields that affected this error: ' + err.getFields());
                    System.debug('The error was caused by the sobject at index: ' + listIndex);
                    System.debug(locations.get(listIndex));
                }
            }
            listIndex++;
        }

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch execute - end');
    }

    global void finish(Database.BatchableContext info) {

        if (currentRecord != null) {

            messages.add('Processing completed');
            currentRecord.Log__c = String.join(messages, '\n');

            if(currentRecord.Log__c.length() > EquixImportManager.getLogFieldLength()) {

                currentRecord.Log__c = currentRecord.Log__c.abbreviate(EquixImportManager.getLogFieldLength());
            }

            if(currentRecord.Log__c.contains('error')) {

                currentRecord.Status__c = EquixImportManager.STATUS_ERROR;
            }
            else {

                currentRecord.Status__c = EquixImportManager.STATUS_COMPLETED;
            }

            update currentRecord;
        }

        if (!Test.isRunningTest()) {

            if (EquixImportManager.getPendingEnqixImports(EquixImportManager.IMPORT_TYPE_ACCOUNT).size() > 0) {

                EnquixAccountImportBatch.batchMe();
            }
            else {

                EnquixOrderImportBatch.batchMe();
            }
        }
    }

    public static Boolean batchMe() {

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch batchMe - start');
        Id jobId;
        if (!BatchUtility.accountBatchInstanceRunning()) {

            System.debug(LoggingLevel.DEBUG, 'Account_Batch_Size__c: ' + Integer.valueOf(EnqixImportCSVParametersManager.getCsvParameters().Account_Batch_Size__c));

            jobId = Database.executeBatch(new EnquixAccountImportBatch(), Integer.valueOf(EnqixImportCSVParametersManager.getCsvParameters().Account_Batch_Size__c));
        }

        System.debug(LoggingLevel.DEBUG, 'EnquixAccountImportBatch batchMe - end');
        return jobId != null;
    }