Thanks a lot for your help.
This time it neither worked to set another folder and "move" the book to it nor set the same folder again. In both cases i got the error: book files could not be moved.
So after connecting i deleted them all under "calibre/device" and synced all again. I have only about 30 book son my device so that's not a big issue.
But what is pretty weird: why do the last 2 folders ".../books/CC/" of the path above simply disappear after the CM-update so that they are not visible any more in file managers?
