What you need to do is to REMOVE the “Log source extension” that is attached to the faulty log source (ESPECIALLY if it is a custom one).
How to do it? Admin > log source extensions > Find the EXT name of the faulty log source > make sure that under “Default for Log Source Types” it is “None”. Then go to log source management, and REMOVE the extension that is associated with the Log source.
This will most likely reset your overrides in the DSM, so monitor it for a few days and set the event id/category parsing as you want it to be.