Time Machine with Mac says its working, but isn't?


I’m backing up with Time Machine.
iMac on Catalina, to EX2Ultra.

Time Machine says it’s backing up, albeit very slowy, and finishes the backup, and reports the backup is finished. But when I try to ‘enter Time Machine’ it will go back only two or three days. All it can see are the ‘snaps’ that are stored in the Mac’s HD, not the true backups on the EX2.

Have others among you found (and solved) this? It used to work reasonably well but has stopped, possibly since Catalina possibly less recently than that.

I’ve tried rebooting the EX2 and the Mac. The Mac can see the EX2 and the Time MachineBackup folder in finder.

Thanks for help