iCloud backup size "0 KB"-- what does this mean?

I have an iPad and am suddenly not sure the iCloud backups are any good.

Maybe 6 months ago I recall checking and seeing something reasonable for the iCloud backups for this device. But I just checked on them like this:

iPad > Settings > (User name) > iCloud > STORAGE: iCloud > Manage Storage > BACKUPS

This lists "0 KB".

Then it lists the iPad specifically ("This iPad") and this also says "0 KB". Under this it says "Backup Size Zero KB". Peculiarly, it does seem to find new things to back up under "Next Backup Size". If I find the "Backup Now" button and do it, the iPad does appear to be doing something and backing up. But coming back to check, the result is still the same-- the total backup size is "0 KB", even after doing a new backup.

Peculiarly, there is *something* under backups in there, because the bar graph, the one at:

iPad > Settings > (User name) > iCloud > STORAGE: iCloud

... does show a small amount of our iCloud space used by "Backup" (yellow bar).

In other symptoms, if I log in on iCloud, I don't see the iPad under "My Devices".

I can't tell if I have a valid backup or not. It could be that the "Zero KB" / "0 KB" indicators are incorrect and there really is a valid backup. (But of course I can't count on that-- I wouldn't want to depend on this backup and try to restore from it and find it to be corrupt.)

What's going on in this situation? Is this "Zero KB" / "0 KB" symptom common? I haven't found any threads in a fair bit of googling that appear to be the same as the situation I'm seeing.