"this file could not be found"

[tmk42066036]

Out of nowhere, lightroom does not rcognizes the files on my exrenal drive. 

After I have updated to V12.0.1. , troubles began to occure. I see all photos under LIBRARY, but when trying to process them in DEVELOPE lightroom shows "this file could not be found". Never changed the location of the files on the external drive, nor changed names of libreries. Also, lightroom indicates that I have zero synchronyzed photographs.

Those are all photos that I have spent hundreds of hours processing!

How can I get things back to normal?  

[Lumigraphics]

Are you on Mac or Windows? Have you tried backing up and verifying your catalog?

https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-corrupt-catalog.html

[JohanElzenga]

One thing to check is if Windows did not assign a different drive letter to this drive, so Lightroom is looking for a drive it knows as "D:" while it is now "E:", for example.

[dj_paige]

but when trying to process them in DEVELOPE lightroom shows "this file could not be found"

Can you find the photo on your external hard disk somewhere? If you can, is it in the same disk and folder as Lightroom Classic thinks it is in? Are there exclamation point icons on the photos and/or question mark icons on the folders?

[GoldingD]

Did you update from v12.0 to v12.0.1

or

Did you upgrade from v11.5 to v12.0.1?