It sounds like a corrupt partition. The scanner may not have prompted you but there must be an option to safely remove the medium. If all else fails, at least wait a few seconds between the end of the last operation and removing the medium. By "a few" I mean at least 30.

Do you need the data or are you happy to reformat the partition and start over? I have always been able to restore lost data but exactly how to do that differs from one case to another so I cannot give you a generic recipe. You must not be afraid to get your hands dirty and dip deep into the command line and sometimes even a binary editor.

The first thing to do would be to backup your MyDocs partition to avoid any more data loss. You will need at least 27GB of free space on your backup medium to do that. Put an empty, large (32GB+) SD card in your phone and run this from the terminal:

Then remove the card. If the data recovery works, you can delete the backup.

Next, you can try fixing the corruption by the easiest method of them all - plug it into a Windows PC and run a disk check on it. If that does not work, look up one of the many threads dealing with data corruption and start from there. Michaaa62 usually gives excellent advice, like for example here.