I always get this with the music library and never with video libraries. I have no other network devices reporting or presenting issues. Passive library updates work perfectly well.
Server (PC Version 1.23.3.4707)
Version 1.33.0.2444-a220eae4
This has always solved it for me. There has been maybe once or twice new stuff just wouldn’t appear. It was in the right directory, and I had scanned everything a few times. A reboot solved it both times.