Quick Links -> Mark Forums Read
I get the same thing.
The easiest work around I've found is to just Log out. That gives me a message saying it cleared my cookies, and logging back in shows the forum clear just as if I marked them all read.
My guess is when they tried to fix the issue that logs people off frequently, they neglected to give that button some different code.
Yeah same here. I was logged out when I opened the forums this morning, so I didn't think to log back out and back in.
I'll try that.
Had to search. Least it isn't just me. Logging out only sometimes works; I check the forums from two different locations and I use the log out feature from both. Hours later or even the next day, inevitably, there will be threads marked as unread starting from posts that I know I already clicked on before logging out. Very annoying for threads that have had dozens and dozens of legitimate new posts and it sends me to multiple pages that I've already seen.
I've already forgotten about most of you

On a whim I tried this again just now.........and it seemed to work. I did not get the page with the quoted jibberish as in the OP.
I've already forgotten about most of you

OK, so whenever I use Quick Links->Mark Forums Read, I get:
"Your submission could not be processed because a security token was invalid.
If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error."
Just started after the forum maint. Anyone else?
"Everybody wants to change the world, but nobody wants to change themselves." -Tolstoy