Problem alternating two external drives on Time machine

I alternate between two external drives with Time machine (Sequoia on an MBP). Time Machine used to handle this seamlessly. Let's call the disks D1 and D2. Now, when I swap in D2, the icon on top reports a failed attempt to backup D1 (and a date for the last backup on D1). The backups on D2 continue to work (according to tmutil on Terminal.

Anyone else dealing with this. It is a nuisance but such an obvious one, I am surprised it hasn't been fixed.