DAV does not work

I am struggling for months to get DAV access to files in Drupal using FF and DAV.
I know that these modules are rather experimental and somewhat unsupported at the present time, but I really don't know alternatives in Drupal ecosystem for a correct handling of files.

I was almost successful for one site, having only some mime detection problems.

However, I am completely stuck in setting up a new site. Almost nothing works.
At some point, I was able to connect to the DAV server and to upload files. I could never add directories
But now, the DAV server is simply not working. The DAV client can't get anything from the server.
I tried several times to disable and uninstall DAV, RDF FF,.... Things are just getting worse.

The other sites still work somewhat.

Any idea apart droping the whole database and start the site from scrach?

Thanks for help.