• The code has 100% coverage in the sandbox with no errors
• Even when deploying from a brand new sandbox I get the error.
• There are no batch calls in the code

trigger TaskTrigger on Task (before insert, before update, before delete, after insert, after update, after delete, after undelete) {
 
    if (trigger.isAfter && trigger.isInsert) {
        TaskHandler.evaluateTasks(trigger.new);
    }
}

public with sharing class TaskHandler {
    // public TaskHandler() {  }
 
    public static void evaluateTasks(list<task> newTasks){
        set<string> didNums = new set<string>();
        set<id> leadIDs = new set<id>();
        for (task t : newTasks){
            if ( string.isNotBlank(t.Dialpad__PhoneNumber__c) ) {
                didNums.add( LeadSourceHandler.scrubber(t.Dialpad__PhoneNumber__c) );
            }
            if ( string.isNotBlank(t.WhoID) ) leadIDs.add(t.WhoID);
        }
        map<string, string> LeadSources = getLeadSources(didNums);
        set<id> LeadsInNeed = getLeadIDs(leadIDs);
       
        list<lead> leadsToUpdate = new list<lead>();
        list<Lead_Source__c> newLeadSources = new list<Lead_Source__c>();
        for (task t : newTasks){
            string didNum = LeadSourceHandler.scrubber(t.Dialpad__PhoneNumber__c);
 
            if ( LeadsInNeed.contains(t.WhoID) ){
                if ( LeadSources.containsKey( didNum ) ) {
                    leadsToUpdate.add( new Lead(id=t.WhoID, LeadSource = LeadSources.get( didNum ) ) );
                } else {
                    newLeadSources.add( new Lead_Source__c(name = t.Dialpad__PhoneNumber__c ) );
                }
            }
        }
 
        if( leadsToUpdate != null && leadsToUpdate.size() > 0 ) update leadsToUpdate;
        if( newLeadSources != null && newLeadSources.size() > 0 ) insert newLeadSources; // save new ones
    }
 
    public static set<id> getLeadIDs(set<id> leadIDs){
        map<id, lead> leadsInNeed = new map<id, lead>([select id from lead where LeadSource = null and id in :leadIDs]);
        return leadsInNeed.keySet();
    }
 
   
    public static map<string, string> getLeadSources(set<string> didNums){
        map<string, string> m = new map<string, string>();
        for (Lead_Source__c ls : [select name, lead_source__c from Lead_Source__c where name in :didNums and Lead_Source__c != null]){
            m.put(ls.name, ls.Lead_Source__c);
        }
        return m;
    }
}

@isTest
private class TaskHandler_test {
    // private TaskHandler_test() {  }
 
    @isTest static void AssignLeadSourcesPrimary_test(){
        insert new Lead_Source__c(name='1234', lead_source__c='source 1');
 
        lead l1 = new lead(lastname='lead 1', Language__c='English', Location__c='Los Angeles');
        lead l2 = new lead(lastname='lead 2', Language__c='English', Location__c='Los Angeles');
        insert new list<lead>{l1, l2};
 
        task t1 = new task(subject='task 1', whoID=l1.id, activitydate=date.today(), Dialpad__PhoneNumber__c='1234');
        task t2 = new task(subject='task 2', whoID=l2.id, activitydate=date.today(), Dialpad__PhoneNumber__c='47');
        insert new list<task>{t1, t2};
    }
 
}