I have a nomination that I upgraded on June 13th. (Nomination was originally nominated June 2nd.) It still have not resolved. Is anyone else experiencing this current issue?
I’ve upgraded a few nominations, some of them take a lot longer to resolve than before ML was introduced. Some of the ones I didn’t upgrade have been resolved after a few days. As it is now it doesn’t seem to matter a lot if it’s been upgraded or not. 
There are many posts on the forum about upgraded nominations taking longer than expected. The only Niantic reply I have seen was this one saying these particular ones are working.
It could just be that there are fewer people reviewing and reviewers having lower rating so that their vote counts for less. So probably working as intended.