How could scan results differ on separate machines?

I know this is a Kodi question, but asking here in case someone knows offhand. I have two RPi2, each running the November version of OSMC. The music library on each device is NOT identical, even though they both point to the same shared music folder (SMB share on Windows 7 PC). How is that possible? I’d assume scraper settings, but I thought music files are scraped from file metadata only?

For example, I added a few Christmas albums yesterday. One of the boxes picked up all of them, and one got them all but one. Seems strange?

I run these devices headless, so the “different” libraries are evaluated based on what I see in Yatse. For both devices, I’ve cleaned library, re-scanned, and re-synced to Yatse a few times - but the conclusion remains.

Maybe the scraper is under high traffic at this time.

Consider a shared library if the systems are identical.