I have had this problem since upgrading to Catalina. I have tried the fixes recommended (shift-command-c) and deleting the plist file to no avail.
I have two network backup disks, one on a Time Capsule and the other on an external drive.
What I have observed is that the process of preparing for backup (with "backupd" running compute bound for hours) will cause Time machine to only see back to yesterday. I believe that is because that is what is available on the local machine. It cannot go back and see what is on the actual backup disks while it is preparing for backup.
When the backup is finally complete, (it finished my 7:42 am backup process at about 5pm yesterday) you can then see what is on the remote devices. For me, one disk had been converted from sparsebundle to backupbundle. What I could see was only what was "upgraded" to the new file type. Later last night, the system finished backing up to the other disk. That disk goes a back a bit further in time. I hope to see all the way back to that time once "backupd" finishes today. Right at the moment I can again only see to yesterday.
The compute bound nature of "backupd" under Catalina seems to be the cause of this issue and its resolution will need to be installed (once available -- I am assuming that someone is working on this) until entering Time Machine will work as designed. In the meantime, you need to see if the backup has completed before entering Time Machine if you want to go further back than yesterday.
