Time Machine issue with NAS after upgrading Sequoia 15.1

Hi everyone, I have a regularly updated backup created with Time Machine on a Synology DS 923+ NAS connected via local network, which has worked perfectly for over a year. Suddenly, for the past few days, after upgrading to Sequoia 15.1, Time Machine seems to no longer recognize the sparsebundle file and is creating a new one, effectively starting a new backup from scratch in the same location.

Just to clarify, if the previous backup was named MyMac.sparsebundle, Time Machine is now creating a new one called MyMac-1.sparsebundle exactly in the same location.

I tried manually mounting the previous MyMac.sparsebundle as if it were an external drive, and it appears to have no issues. A disk utility check came back positive, and if I access the sparsebundle through Finder, I can see all the files and folders inside and even manually restore files from the backup. Despite this, Time Machine refuses to reconnect to it and starts the new backup instead.

Any suggestions? it looks like that lot of people out there are experiencing issues with TM after migrating to Sequoia. Everything was fine with 15.0 for me, issues seems have started with 15.1. The usual fix adopted for 15.0 (turning firewall off) does not work on 15.1 and, in my case at least, I had no problem with 15.0.

I know that primary fix is "delete and make a new backup", but this the very last resort for me, as I have 2Tb data on iCloud which should be downloaded by TM for creating a new backup from scratch, that means days of work, a very time and resource consuming solution, and above all I should leave home my MBP waiting for TM to complete that new backup, not to say that then there were no guarantee it would work in the usual incremental way.

Carlo