Time Machine backup fails and cannot browse previous backups

Time Machine History not browsable and backup failure

Tahoe 26.2, LaCie 4 TB disk, APFS (Case Sensitive), USB-C connected. Lots of free space.

After a surprising failed backup where it complained that an old little file "could not be backed up", I entered Time Machine to Browse its Backups. To my horror, it showed zero backups older than today! I cannot browse backwards despite there exists backups since 2021 that recently have been accessible and working without problems.

That little file which it complained that it could not back up is NOT the problem, since if I remove that file it will complain about some other old file. The real problem appears to be that Time Machine cannot recognize available history, which makes it appear to be corrupt despite it is probably some linking that is lost.

Steps I've tried:

• Restart Mac from shut down
• Reconnect TM (and it is set to Manual backup)
• Disk Utility First Aid of the TM disk volume
• Have checked that System Settings > General > Sharing > Local hostname is unchanged.

Meanwhile, if I use the Sidebar in Finder and click the mounted Time Machine volume (which clearly has a Time Machine icon), I can see backup dates going all the way back to this computer's very first backup in 2021.

While this volume window is in the foreground, I can click the "Enter Time Machine" button in Finder, or use the Time Machine menu to successfully "Browse Time Machine Backups". Suddenly, Time Machine's interface seems fully functional. From this point, I can browse to whatever files/folders I desire to recover. I thought this had solved the problem, but if I go to a particular folder on the startup disk and then enter Time Machine, it will show zero history beyond today!

Steps I've NOT tried:

• Some people have suggested that one can use Time Machine Settings to Forget this backup destination and then add the same thing again. However, I have been reluctant to do that since I am afraid it can make things worse. What is your experience and recommendation?

Similar error was discussed in https://forums.macrumors.com/threads/time-machine-not-working-to-see-back-in-time.2399852/ but no real solution.

Do you know of any solutions to this problem?