Strange behaviour of ISNEW in Validation rule

Question

On the Opportunity object i have a validation rule as follows

AND (

     NOT(ISNEW()),
     RecordType.DeveloperName = "My_Opportunity",
     ISNULL(CustomTextField__c)

 )

The goal is to allow the creation of a new Opportunity Record of a particular record type even if the CustomTextField__c has a bkank value. However, after the record is created, when a user edits the records, the CustomTextField__c must have a value to be able to save the record.

Now here's the strange behavior, this works perfectly for a user in the 'System Administrator' profile. However for other users the validation rule fails - the new Opportunity record is not created. The error is -

'We can't save this record because the “Opprtunities” process failed. Give your Salesforce admin these details. This error occurred when the flow tried to update records: FIELD_CUSTOM_VALIDATION_EXCEPTION: Please enter the CustomTextFieldValue'

Answer 1

I found the issue. I have a Process Builder to update a field in the Opportunity record 'after created or edited' for the Users in Non System Admin Profile.