@Azi Is it a native Mass Update? Or a scripted one?

@erictgrubaugh It is created in Netsuite (not code) and run on a schedule

Maybe only scripted mass updates fire "Custom Mass Update"

@erictgrubaugh Hmm. That could a real issue then. How would I be able to exclude it?

although it sounds risky, you might want to exclude the USEREVENT execution context

you might also try excluding context.type = 'xedit' as an alternative

What @battk is correct. User Events should not trigger other User Events. That being said, @Azi wants the script to fire when the record is submitted by a user event, but not in case of Mass Update. How the user event is triggering other user event, is still a question I am wondering about.