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.
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).
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.