Your logs show files being processed normally, it’s probably just taking a while to process all the files.
Correct. It has nothing to do with mono, the source file name has Mono in it though.
Normally this would be something with where Sonarr was compiled from, but this is something configured on your system as a volume that Sonarr is trying to resolve.
A mount with that path should not exist, something seems misconfigured on your system.