I had to disable the rich text editor in my preferences to see a reply box at the bottom of threads today. I don't know when that started. The last reply I made with it was on Wed. the 29th.
Lazy, so just pasting in a comment from my other glitch report
Fixed, now.
@UncleJunkle 's tip here Cookiebot Settings Break ECF Functionality in Firefox seems to do the trick. For a lot of issues that cropped up after the migration. (At least for me, both problem and fix.)
Since it seems to be part of the board conglomeration and not my end, I'm just a tad confused about what changed it, having had no board issues for quite a long time. Maybe some incompatibility between Xenforo and the app?