@Stefan and @Flox Just to let you know that as of the just released Rockstor version 3.8-14.02 testing channel updates contains the code changes that are intended to help with the problem that I think you have both encountered, ie occasional boots resulting in empty data mount points, which a reboot then restores. If all is well these changes should be included in the next stable channel update but are available in the testing channel if you wish to provide any feedback on if your systems are still displaying this behaviour once running 3.8-14.02 or newer.
Thanks and just to let you know that there is hopefully a fix awaiting testing; and if not then at least the logs should be of greater value given they should now contain more descriptive device names.