I think I found something. The grouping is not allowing us to change it anymore.
Clearly, we're supposed to have multiple options but there's only one now.
The first field has always been a toggle 'Album Artist' on/off as being a criterion for grouping.
You're supposed to use lines 3 and 4 to have multiple options and refine your grouping criteria.
But if I use lines 3 and 4, Monstercat for example get 69 albums instead of 2 and it doesn't solve my problem of compilation albums not showing up under the contributing artists' pages.
Here's a screenshot mockup that I made to try better explain what I'm talking about that's not happening :
These two tracks are made by Pegboard Nerds, right?
Therefore, that same album should appear under Pegboard Nerds' page...but it's missing.