This is an issue with the Brain database, not TheBrain app (we just released version 18.104.22.168 by the way). Please try restoring your Brain database from its automatic backup.
When TheBrain accesses a Brain database, it automatically creates a backup each time the Brain is opened. Note that this backup is not a substitute for a full backup that should be done using TheBrain Cloud Services or the Create BrainZip option as it does not include any of the attachments and other data that is not contained within the Brain database directly.
In order to revert to the automatic backup, the _brain folder will be needed. This folder can be found where your Brain database is stored.
Reverting to the automatic database backup:
1. Close TheBrain if it is running.
2. Backup the _brain folder in case a problem is encountered during the reversion.
3. Open the _brain folder and find the brain_db folder.
4. Rename the brain_db folder to brain_db_old
5. Reopen TheBrain and open the Brain that is being restored.
6. Let the restoration process continue and complete.
If you are still having trouble after this, please let me know.