After looking your video, we got that the problem is not coming from wpForo, that's because wpForo doesn't do any changes in Dashboard > Users and Word Press Roles. We saw that you have several plugins Like Buddy Circle, Buddy Boss Etc. We suggest you first find out the current plugin which creates that user role, after that contact to the plugin support team. You can try to deactivate the plugins one by one to find the needed one.

https://www.loom.com/share/6380e1fd705c46d0885ac3238ed27438

If there is no participant user role, so how did your users User Role changed to not existing one.

Can you please explain to us what do you mean saying participant, maybe we hadn't understood you correctly?

See screenshot.  It is set to Customer

I checked all user roles and none of them are set to Participant.

Check the screenshot above.

https://wpforo.com/wp-content/uploads/2021/08/wpForo-New-User_Default-Role.png

I don't see this anywhere........

The problem can be from that you have chosen New User Default Role - Participant in Dashboard > Settings > General because of that all of your new users have been registered as participant.

Or you have changed one or several wpForo Usergroups User Roles from X to Participant, which has changed your 120 users from X User Role to Participant

Yes I read this and understand how the UserGroups work - I just don't understand why suddenly I have 120 participants when I have not setup anything to do with participants either in WP or WPForo.

Read this topic about wpForo Usergroups, Forum Accesses and WordPress User Roles, if it won't help you let us know.

https://wpforo.com/community/faq/wordpress-user-roles-wpforo-usergroups-and-forum-accesses/