With troubleshooting mode you mean debug mode? https://wordpress.org/documentation/article/debugging-in-wordpress/
That would be a good way to start yes, if you have a local or test setup in which you can reproduce the exact same error, I would try turning plugins off one by one there, to see if it is being caused by any of them.
Errors like these can have many causes but the template for this particular page is at
/bbpress/templates/default/bbpress/user-profile.php
What you’re referring to is not an e-mail, its the user slug (hence the reason the @ symbol gets removed and a dot becomes a dash) the slug is the path used in the address bar to identify the user by a url so it cannot contain special characters.
Hi, as the author of the plugin I can confirm it indeed was a bug, sorry for the inconvenience and thanks for reporting this! it has been fixed in version 1.0.3 and upwards.
