Unknown error "Please select a form and try again"

I am receiving an error "Please select a form and try again" when some users (I believe that so far they are all authenticated) are submitting tickets after completing all necessary fields. I can't find any documentation on this error and Zendesk support hasn't been able to assist.

When I opened a support ticket they indicated the error is happening was because we had modifications to the Copenhagen theme - mic drop. However all modifications were made more than a month ago, and only some of the forms are affected and have only been so for the last 5 days.

I need assistance troubleshooting the script.js (the only modified portion of the site). It's currently modified to hide some menus when a user doesn't meet two criteria.

Currently I am using Notepad++ to look for errors in the code and can't seem to find any breaks; according to the formatting the code flows top to bottom the way it should.

How would you recommend I begin to debug?