Hi.
I'm using 1.14.3 and had a mandatory field (user title eg. Mr, Mrs etc.) added to the contact information form.  This was disabled and not showing up in the form itself, as expected, however the mandatory flag was causing account creation to fail completely, even though the field was actually disabled and non-visible.
We've always had reports of difficulty signing up for accounts on our system, to the point where we disabled registration requirement as I couldn't figure it out.  I just found this thread:
https://forum.osticket.com/d/95604-resolved-api-new-ticket
And it made me think to check the fields... upon unticking the disabled field as required, the registration process now completes.  That other thread dates back to 2019 so this issue appears to have been around for some time - I haven't had a chance to test 1.15 yet.
Thanks.