So it seems like it could be a plugin at this point. Try turning on Restricted mode (no community plugins) and restarting. If it’s alright then, you can turn off Restricted mode, turn off all plugins, and go one-by-one or in batches turning them on to find the culprit.
All of these steps are in the forum template, the troubleshooting link/debug link, before you post in the Help category.