Field Assignment not working just on one custom field

I created an event which isn't actually an event but rather an item that people can buy. It's all working fine, except the very first custom field I ever made refuses to let me use the Field Assignment of "All Events Except Those Selected." I thought it was the particular 'event' but it just won't accept anything. It says it saves, but it's just reverting to the original "All Events."

What I'm doing:
- edit custom field first_name
- under 'field assignment' choose 'all except selected events'
- choose literally any event
- click save

It reverts back to field assignment 'all events'

I have tried this in Chrome on mobile, Chrome on desktop and IE on desktop; it doesn't appear to be a browser issue. I have also changed a number of other custom fields to exclude this or other events and all were successful.
I have tried unpublishing it: it won't unpublish. I have tried deleting it: it wouldn't delete (which in hindsight is a good thing).

Any ideas on this?
I would send a support ticket but my website has IP restrictions and it's not easy to let you in: I will if there's no other option.

Thanks,
Melissa

Hi Melissa

It's how the extension is designed to work. The first_name (and email field) are two special fields and need to be enabled for all events. That's why you cannot change it

Tuan