Troubleshooting Data verification errors

Do you see any errors while the INC job is running? Are all these systems running on the same media agents? Did you narrow down the jobs converting to full to a specific media agent or storage pool?

There is a lot of information missing here, but I would start by looking at the event logs on the job that converts to full.

This is not good. Its an automatic protection when data verification fails - either at the job level or the incremental DDB verification. DDB verification can mark blocks on disk as bad, a full backup ensures that a new baseline set of data is created, otherwise all your backups might be unrecoverable forever if the synthetic full is referencing missing or damaged blocks.

Check out the admin job history and look for any verification jobs. There should be events on the job with more details. There is also job based verification - add or look for the verification status column in the backup history

If you can’t find the source of the issue, please open a support case - as dude said, there are many variables and likely will require some analysis in the logs.