I had the same issue after latest CSSU-testing (non-thumb) update. The issue was certain config file (that controls mounting of MyDocs) was not properly replaced by the CSSU-update. You might want to check the CSSU-testing thread for more details.

EDIT: The delay to remount MyDocs after reboot is normal: There is now fsck.vfat process that checks the filesystem after boot before it mounts MyDocs. If you have lots of files in MyDocs this easily takes few minutes...