Validate Database tool does not appear to recognize MapUnits in MapUnitPolys, throws Lvl. 3 error regarding map units "not in map"

[MnashUSGS]

I have a geodatabase that contains all the necessary elements, including map units in MapUnitPolys. These same units appear in the .gdb's DMU.

When I run the validator, it throws this error.

I have tried the following, with only infrequent success:

1. Restarting ArcPro - Doesn't seem to work, still throws error
2. Opening up the .gdb in a new map project - Seems to sometimes throw error
3. Opening up the .gdb in a new, blank, untitled project and running it only from the Catalog pane - Worked, but I only did this once and have not tried it again.

I do not know what causes the script to sometimes not recognize the map units on the map. Does it read Field: MapUnit in MapUnitPolys?
The MapUnits it does not recognize don't seem to have a particular trait - but it appears to mark the majority of the units in my map (~75%) as "not appearing on the map".

[ethoms-usgs]

I think your #3 attempt is telling. In the other cases, are there layers based on GeMS feature classes from other gdbs?

[MnashUSGS]

In the other cases, I don't have any layers based on GeMS FCs from other gdbs, either in the .gdb which Validate Database is checking, nor loaded on the Map Frame.
For my #2 issue, I'm not entirely sure what causes it to work sometimes and then not recognize MapUnits other times, although I wouldn't say I've done that test more than 4 times at this point.

[ethoms-usgs]

Can I get a copy of the gdb?

[MnashUSGS]

Sure, I'll email it to you