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.
Nothing changed.
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.