April 4, 2020 9:29 EDT AM
I have a few Macs backing up to two Synology drives. I use both Time-Machine and Carbon Copy Cloner. I had intermittent problems with CCC and I eventually found some advice on their site that for backing up from Catalina, one should format the backup drives to apfs. So I did just that and most of the unreliability went; I am now on my final, final tests and then I will just leave it to run to see what happens. All the drives on on the Synology kit are rotational.
CCC have just issued an update, though. It referred to timing issues over backups and that may have resolved the final problems.