Update: Oh, nicht nur bei mir...
...sondern weltweit: „following and followers all lost“.
Twitter dazu: „We’re still in the process of recovering from the missing follower/following problem that occurred earlier today. Over the next several hours, you may see inaccurate counts or timeline inconsistencies as the correct data is propagated to all parts of the system.
One thing to note: Even after this recovery is complete, your counts may appear lower than previously. In almost all cases, this is not due to missing data. The counts we display on your profile page are not always up-to-date. For example, when we remove spammers from the system (which we’ve been doing a lot lately), the follower counts are not updated in real-time.
As we push out the changes to fix this afternoon’s problem, the counts will be updated to reflect the latest numbers.“