This problem is ongoing, and struck a second time for me today. I was removed from all groups (except the Commons), and, for the second time, all my Activity was erased (the ongoing list).
I didn't notice there was a problem until I had replied to a group post and then tried to edit that post afterward, only to face a blank screen. It wasn't until I "re-joined" the group that I was able to edit the post I had made.
Now the two blogs I created do not appear on any list (Dashboard menus, main list of blogs, etc.,).
http://community.mises.org/stevendouglas/ (the first one I created)
http://community.mises.org/fedup/ (the second that I created after the first disappeared from all references)
Note that I can get to either blog following just the URL, but there is no reference to it on the main Mises site or any of my Dashboard menus.
I know this is affecting others, because the group membership numbers, as well as the total list of available blogs, are altered in the process.