Multiple pages of "Show unread posts since last visit" disappearing

This has been occurring a fair amount, and has been discussed by the Moderators.

When viewing the "Show unread posts since last visit" (where there are several pages to view), suddenly they will all be gone.

Prior to all logins being https, I frequently used the encrypted side of the forums, so that when working thru the unread posts, the list would auto-refresh and ones I had viewed would disappear from it; I thought perhaps it was related. What typically would happen is that when using the mouse-button to go back to the list, Firefox would freeze, becoming non-responsive; eventually I'd have to shut it down. Log back in, and the list is down to one page, or gone entirely.

This just happened again (it's been a few days). There were four pages in the "Show unread posts" list; FF locked up and had to be terminated. Logged back in and the attached screenshot is what I saw.

This normally happens later in the day for me, when there are the most # of users online (and more Mods active than at other times). I note we have 89 guests and 26 users online right now.

LM