Hi there!
I seem to have a similar issue as this poster here: https://simple-press.com/support-forum/sp5-general-topics/unable-to-reply-or-create-a-new-topic-at-all-not-even-admin/
This was brought to my attention today before I handled any updates. Noticing there were SP plugins and a theme to update, I did all that plus WP, WP plugins to see if that could be the issue. But they are still not working. I also gave this a shot too but no luck
https://simple-press.com/documentation/codex/faq/troubleshooting/my-forum-display-is-unformatted-after-an-update/
Could you please take a look?
website: http://www.yoga-teacher-training.org/forum/
Thanks!
Meredith