I use LR file manager as told to and it pops up dialog saying file lost. Huh?

[Dave Rye]

How does the file get lost by Lightroom when moved from one folder to another using LR Folders drag and drop in LR Library module?  I used LR instead of trying to use Explorer or suchlike to avoid this sort of thing, but the DB must have gotten corrupted by LR itself.  It doesn't even show the file it lost or a option to relink it in the collection it WAS in.

[dj_paige]

Without further details, and some screen captures, it's really hard to advise.

Show us a screen capture of your Lightroom Classic Library Module, so we can see the photo in question, and what folder Lightroom Classic thinks the photo is in. Then show us your operating system of the ame folder so we can see what is in there.

[Rob_Cullen]

When you say "lost by Lightroom" are you saying the Preview is marked with an exclamation mark [!] or the preview no longer exists anywhere in the Catalog?

Is it possible you are 'dropping' the moved file to a folder that was not the intended destination?

If Lighroom-Classic says a file is missing [!], then the Catalog database does not have the right location data to find this file.

Several things will cause files to be 'Missing' [!]-

Files or folders- Moved, Renamed, Deleted, in any manner outside of Lightroom.

An external drive that assumes a different 'name/address' when re-connected.

"in the collection"

If you mean a Catalog 'Collection'- Collections are not 'real', they are 'virtual' lists of photos. (Like a grocery shopping list of items you want from the store.). They are not related for the location of files in folders.

Post a few more details about what you are seeing and how you are 'moving' files.