Compilation/artist album mix-ups

There’s something going on with compilations in my library that I can’t figure out. Maybe somebody here can help?

I’ll use one example, but this sort of thing is happening all over my library. In iTunes, I have these three albums:

Slim Harpo ‎– The Excello Singles Anthology (44 tracks)
Lazy Lester ‎– I Hear You Knockin’!: The Excello Singles (30 tracks)
…and a compilation: The Best Of Excello Records (30 tracks)

The compilation contains a fair number of tracks that are also found on the other two artist albums. All 104 tracks have been tagged carefully, completely, and accurately in iTunes.

In my Roon library, none of the three albums is complete. Worst is the compilation, which only lists four tracks. It seems that Roon has decided “he has this track elsewhere, so I don’t need to display it as part of this album.” Even worse, Roon has sorted some of the compilation tracks onto the artist albums, and vice versa. Bottom line: it’s incomplete, and it’s a mess.

I’ve tried retagging everything exactly according to Roon recommendations. I’ve done that twice: once in iTunes, and once using tagr. I’ve tried re-scanning, re-identifying, and “fix track grouping.” Nothing has worked.

Is there some setting I’ve missed that’s causing this to happen?

Thanks, Roon Community.

2011 MacBook Pro, 8bg RAM
OSX Yosemite 10.10.5
Roon 1.2 (build 165) stable (64bit)
Music is stored on an external USB 3.0 drive, connected via an OWC thunderbolt dock.

UPDATE: I just added the same three albums to my library at work, and they set up perfectly in Roon here. At work, my more limited library is stored directly on an iMac’s internal HDD.