Active Backup for Business - previous snapshots of C:\ not found

Hi all, I encountered on 2 of my laptops a problem which causes me a lot of frustration as via the Synology forum I really can’t solve it. I’m using a DS216+II with 1GB RAM and 2x 8TB HDD. Suddenly instead of doing a normal incremental backup I got the message ‘previous snapshots of C:\ not found’ in the agent screen which repeats itself continuously and a complete backup is now running for a very long time (386GB from 1 laptop). The Hyper BU can’t start as this proces is going on and no other laptop can now do a backup. I really did all the recommended steps what Synology asked but it runs still the full backup and causes delays for all other services. I cancelled Hyper backup temporarily to give max. resources. 1 issue I found too but didn’t do is to increase the RAM of the NAS but you loose your warranty at Synology. Did somebody else encountered these issues too? Does somebody have recommendations / solutions? I’m desperate now as I have it for the second time.