An interesting workaround which I have had success with recently is the top left of an active thread that you have been reading is the shortcut ‘View First Unread’.
This has consistently taken me to the ‘hidden’ last page, after which the thread becomes normally readable.
The shortcut is only there for threads that you have followed previously and which has more posts since your last visit. Not ideal but another solution when faced with this perennial problem 👍