If users A and B are looking at the same thread with TOC on, and user A creates a new message, then user B seems to be unable to scroll to that message by clicking on it in the TOC.
This has been around a long time but it was hard to reproduce. Two users and newly created message seem to be crucial. (Undeleting a previously deleted message doesn't seem to trigger it.)
Update: I can no longer reliably reproduce this. ☹️
If users A and B are looking at the same thread with TOC on, and user A creates a new message, then user B seems to be unable to scroll to that message by clicking on it in the TOC.
This has been around a long time but it was hard to reproduce. Two users and newly created message seem to be crucial. (Undeleting a previously deleted message doesn't seem to trigger it.)
Update: I can no longer reliably reproduce this. ☹️