That's a mother file yes...
If you mean that a mother file (folder?) is the parent folder, then I've not come across that term, which is why I asked.
...they disappear completely - but not all of them.
So some folders disappear from the folder list on the LH side of Library module. You can see the parent folder and some of the folders in that parent folder, but some disappear. All trace of the files in those folders is also lost from the catalogue, so you can't even select the top level folder and search for the file name?
I'm struggling to think of causes of that, such as:
- Lightroom is opening the wrong catalogue, or an older version of the catalogue.
- The catalogue file has become corrupted. This seems unlikely as LR generally detects corruption.
I've never experienced that, nor heard it mentioned in any of the forums I've looked in.
It doesn't sound like an operating system issue or a disk fault. I mean: if anything outside LR had moved, deleted or renamed the folders, then the folder would still be in LR's list, but with a "?" by the name.
You can check the catalogue for corruption (in Windows) when you start LR by double-clicking the LR icon, and immediately pressing and holding CTRL, ALT and Shift together. It gives you the option to check catalogue integrity. Or you can go to Edit -> Catalog settings -> General tab -> Backup and select "When LR next exits" and check the "test integrity" box. I don't know if it's the same on a Mac.