Lightroom catalog suddenly without images

[Colorful_play0D45]

My catalog suddenly shows only 15 images, although more or less than 10,000 images have been edited.
In Windows Explorer its size is 198 MB with the same catalog name 2-2-v13.ircat as in Lightroom. Aren't catalog size and number of images completely contradictory?

The previous catalog version 2-2-v12 is dated 12.10.23 and has a size of 196 MB.
The latest backup 2-2-v13.zip is saved on 09.12. and has a size of 204 MB.

Of course, I have never handled the catalogs recently, except that I work with a weekly backup.
Before I destroy all the editing steps, I hope someone can help me with the procedure.

[GoldingD]

Sounds like you upgraded LrC from v12 to v13. And as a result, upon starting LrC it upgraded your previously used catalog.

HOWEVER

 Sometimes that upgrade of the catalog, upgrades the wrong catalog, or even upgrades no catalog (creates a new one)

Users with this issue see a catalog that is either missing many photos, missing latest edits, or is in fact empty (new)

This has never been clarified as a bug, or a file problem, or a hardware problem. I suspect a corrupt preference file.

Typical solution is to use your OS File Browser  (Windows File Explorer in this case) to look for, find, and use the correct catalog (pre v13), by double clicking on that catalog.

P.S. When you open that catalog, and LrC tells you that it wants to upgrade it, You might want to alter the file name as to dump all those extras number 2, just saying)

[Colorful_play0D45]

@GoldingD

Thanks for checking my problem.

Let me describe first what I did in the meantime.

I gessed, too, that a wrong catalogue was picked up by Lightroom . 
I extracted the latest ZIP-File from my Backup and then selected Files > Import from other catalogue using the extracted catalogue file. 

Unfortunately, from about 12.000 photos only about 11.000 were found. I obtained a text protocol showing the missing 1.000 files called „import failed“. The Backup which I selected dated from Dec. 09.  At the time I made this backup all of my files were still imported, I guess. I would now try with the next oldest backup dating from Nov. 23. Would this be acceptable?

Now coming to your recommendation.

The previous upgrade v12 dates from  Oct 12 being way too old. Is there any difference between taking over that catalogue or any one from my weekly backups, as I did? You suspect a corrupt preference file. Where should I find it in the Windows explorer and would there be a way to restore it or find out what is corrupt?

Is your recommendation to doubleclick on a catalogue the same as what I did by choosing files > import from another catalogue?

I would be very happy to receive your answer.

[GoldingD]

Search for all .lrcat files on that computer. Are you sure the most recent catalog is where you looked?

[Colorful_play0D45]

I could settle the problem. Apparently the mess happened already after the second-last backup.
It seems I had overlooked the missing imports at that time.

Again I learned something more due to your help. Thanks a lot.