MC 29 on Linux in Docker here. Was tearing my hair out trying to sort out an import issue, but it may actually be a bug.
If you attempt to import a movie file that has an associated .nfo, but JRiver has no access to the outside internet, it will not pull any relevant data from the .nfo and has a tendency to throw the mkv / movie file in "Documents" not "Videos" category (which can of course be overridden by type and subtype tags), yet it places the .nfo in "Videos".
This was fixed by changing the IPTable routing to allow outside connections for the import of one movie. After that, with the IPTable routing set to drop all connections except for local, further movie imports seem to work fine and pull data from the .nfo, the expected behavior. This was tried multiple times with new configs each time, the only way to get it working was allowing it to connect for a single movie import and then turning off access again.
Strange.