Your comments

This option only appears in the admin user interface. Normal user doesn't have this option. Right?

Yes, I know, but, manually?

When you made the mistake of move files out of interface, what are the steps to set FileRun "OK", I mean, DB, index, thumbnails... What command-line tools and in what order.

Or I have to go to fresh install?

I have FileRun on docker. System, db, and HTML in SSD, and files in HDD.

And I browse folders with hundreds of images very fast.

Would be appreciable the speed increase in this cases changing to an SSD?

Sorry,  I know that it's not about FileRun issue, I only ask for suggestions.

Thank you.

thats seems a permissions problem. 

It is under docker?

With a file explorer that supports WebDAV connections. It's not an app that can upload files automatically, for example.

I had a similar issue, but with other WebDAV client, and I solved it with the @Home.

Have you added @Home to the WebDAV path?

Do a "ls -l" command in the folder to see what happen with this file.

I had to do a chmod and chown to solve a similar problem.