When I see this error, is there any way to see more of what might be causing it, without contacting support?

Can share some details on how this error was presented? record type, inputs, execution context etc

User event script in an after submit, running on a "case record" does a submitFields on a customer record

does your user event script have fields being set also on the before submit function as well as the afterSubmit submitFields which you mentioned? I would be happy to take a look at your code if you want to share it

Sometimes using a different browser gives you different error message

@Sandii Weird. In Microsoft Edge, there is no error altogether. Only in chrome

Excellent work

🤣