I have been required to delete my back up folder on my synology NAS at least 10 times.
Time machine fails at every attempt. I can establish a backup easily, but it always fails after 2-60 days. All the other computers on the network are working well. This happens whether wi-fi or ethernet is used and is not related to upgrades or other disruptions that I can see.
Only one device on my network does this. After establishing a successful backup which lasts days, the time machine program then "loses" the relevant sparsebundle and cannot be rejoined. Attempts to do so have suggested that this is secondary because back up then proceed for 20-30 GB then fail. The primary trigger is beyond me.
iMac 27″ 5K, macOS 12.1