Hi,
Thank you for posting in Symantec community.
As of now I have not seen any known issue with SEP 12.1 RU4 MP1a DB.
Verify database maintenance options are selected like Truncate transaction logs and Rebuild indexes.
Could you repair the SEPM?
100 GB disk space is recommended however I would request you to keep it under observation, if database size keep increasing we can conclude that database maintenance is not happening in the background.