I have tried 4 different MU clients on my iphone. MUDrammer is hands down the best. Like, way way way better than the others, which have some really redonkulous stuff, like constantly sending y+accent, or not allowing you to recall what you've already sent.
It also happens when the notifications are directed towards you but not at you. So @Arkandel@Rook ing you should do the trick if you mark all as read now.
This topic was briefly locked while I split it up. It's open again. I'm going to move it to the Suggestions area, since any original Announcing is long since past.
This has happened to me in the last couple days whenever I've tried to upload an avatar to my account. The uploading ends in a 502 error, and then I can't access the whole site for a minute or two (or more).
I tried turning some of the plugins on and off to see if it was that, but that doesn't seem to be the case. For now, you'll have to use the url bar to navigate if you're on mobile.
There's my userscript (over in Userscript for Ignoring Users and/or Threads) but since that's clientside the board still pops notifications and therefore still needs to be marked read, so it may not help a lot for this case.