Ah, it’s bbpress – normally a good choice. I’ve installed it on one of my sites to test, and some settings you may want to try: Settings, Forums.
The only thing in its settings that might be worth changing is to toggle Fancy editor
If not, try disabling other plugins one at a time to see if they fix it. Especially any editing plugins you may have.
Then change to a different theme.
It can take a fair bit of time and faff to sort, unfortunately. 🙁