This may be brought up elsewhere, but I've tried to give it a clear title.

Currently, when setting overprint to 100k strokes (for example), Illustrator may not display/apply the overprint for grouped objects, making the user have to find the erroneous objects, then ungroup them.

Overprint slows Ai down a lot, making this task a real headache, so it'd be lovely if this were sorted in the menu.