How many catalogs have you got? Most people use one.
Must admit I would have the same reaction: how is it possible for Lightroom to lose a catalog?
Are you saying that one day you close Lightroom normally and everything is OK. Next day you open it and your catalog is gone?
Which version of Lightroom? Which operating system? Where do you store your LR catalogs? Why do you have multiple catalogs?
Like Sunday, I uploaded some RAW files, and pulled them into lightroom and everything was still there from previous. I went to re-edit some collections from before and all of my collections, were gone. My work catalog was gone completely, but the Personal was still there with only the two shoots I uploaded on Sunday. The rest of the collections were gone completely.
I had Windows 8.1, and it happened twice. I upgraded to Windows 10 here recently, and it's happened again. The
I just have the two catalogs, Personal, and Work. Personal on the C drive and Work on an external drive.
I have/had the latest LR as of today.
Is the drive letter or device name on the external drive changing?
Have you actually looked at the external drive and double-clicked on the .lrcat file to open it?
Work on an external drive.
I suspect you may find that to be the issue.
Is the drive letter for the external drive changing?
Re-connecting to the Work catalog should be a matter of following the steps in this FAQ
It sounds to me like you are opening a new catalog (or different catalog) each time.
Do you sometimes launch Lightroom by double-clicking on the Lr icon, and other times Lightroom launches automatically when you insert the camera card into a card reader (or attach the camera via USB cable).
Can you explain what you mean by "My work catalog was gone completely"? Does this mean the file doesn't exist any more and you know because you used your operating system's search feature and didn't find it? Does this mean that when you open Lr, you don't get your work catalog? Does it mean something else? Give us the exact details of what happens that leads you to state "My work catalog was gone completely".
You have a workflow problem.
Lightroom is at start looking for the catalog it last opened. If that "moves" you will get a message telling that the catalog has not been found and Lightroom suggests opening a new one.
If the catalog is located on an external disk, it is probable that Windows allocated a different drive letter. This happens all the time, especially when you plug-in different drives in different orders each time.
If this happens, locate your drive and open the catalog at the new location. Only work around to this is to attribute the drive a high drive letter, as windows allocates those from bottom to top automatically. Windows changes the drive letter, when some other drive has taken the formerly allocated one.
Generally speaking, I suggest you read first this: Photoshop Lightroom catalog FAQ
If you still have questions on the catalog, please come back.