dear jay,
i have implement your code above, but still getting error when i auto-convert the second lead :(

got the error 
Error element myRule_1_A1 (FlowActionCall).
An Apex error occurred: System.DmlException: ConvertLead failed. First exception on row 0; first error: DUPLICATE_VALUE, duplicate value found: []

on the apex : 
Public class AutoConvertLeads4
{
    @InvocableMethod
    public static void LeadAssign(List<Id> LeadIds)
    {
       // List<Account>  paccountemail = new List<Account>();//adding this #1
                List<Lead> leadList = [SELECT Company FROM Lead WHERE Id IN: LeadIds];
                Set<String> companyList = new Set<String>();
                
                for (Lead l : leadList) {
                    companyList.add(l.Company);
                }
        
                List<Account> accList = [SELECT Name FROM Account WHERE Name IN: companyList];
                Map<String, Id> mapOfAccName = new Map<String,Id>();
                
                for (Account acc : accList) {
                    mapOfAccName.put(acc.Name, acc.Id);
                }
         
        LeadStatus CLeadStatus= [SELECT Id, MasterLabel FROM LeadStatus WHERE IsConverted=true Limit 1];
        List<Database.LeadConvert> MassLeadconvert = new List<Database.LeadConvert>();
        for (Lead l : leadList) {
                            Database.LeadConvert Leadconvert = new Database.LeadConvert();
                            Leadconvert.setLeadId(l.Id);                
                            Leadconvert.setConvertedStatus(CLeadStatus.MasterLabel);
                            Leadconvert.setAccountId(mapOfAccName.get(l.Company));
                            // Leadconvert.setDoNotCreateOpportunity(TRUE); Remove this line if you want to 
                           // create an opportunity from Lead Conversion 
                            MassLeadconvert.add(Leadconvert);
                        }
        
   //     if (!MassLeadconvert.isEmpty()) {
     //       List<Database.LeadConvertResult> lcr = Database.convertLead(MassLeadconvert);
      //  }
    }
}

on the process builder : 



sorry im beginner in apex code..