Very often, but not always, clicking the permalink of the 30th answer on some page (using whatever sorting), gets one to the page after that answer, where then obviously the
#anchor of the linked answer does not exist. Hence, it seems like the link refers to the question instead of to an answer.
It happens for all three sorting methods, though testing for sorted by vote might be a bit difficult as people might cast a new vote during testing... (Testing with some old question might help, but now that I link to it, it might get some attention again... Just choose whatever sorting you like, then go to the 2nd page, and click the permalink of the last answer for that sort order. You'll get to the 3rd page, for all sorting methods.)
I figured maybe there's a difference whether or not an answer has been accepted, but it does not seem to matter.
Sometimes it only shows from page 2 and up. Maybe things are affected by deleted answers as well (which I cannot see, but the 10k's might see different behaviour)?
Of course, the issue is not about clicking the permalink shown beneath the answer itself, but following that very same URL from some other post, or from the activity notifications. Am I right to assume that, with 30 answers per page and 3 sorting methods, in a worst case scenario 1 out of 10 permalinks might not work for part of the audience?
(It feels a bit like "Random sorting appears to screw with answer permalinks" but that was caused by true random sorting, and is fixed.)