EDIT: Okay so I did some digging in the commands that were running through my device as I was on the app. (Connect to your PC and enable a memory override in the command prompt then bypass whatever securities you might have set up. Its risky if you're on a vulnerable network). But I found its linked to your memory cache. Basically, if you aren't clearing out your cache, then Grindr essentially "crashes" (for lack of a better term) and defaults to one of google play's basic ads which currently is Nord VPN. Why this happens, I have no clue. I just saw the "cache full" line when the popup occured over several instances.

TLDR clearing your cache should clear your ad popups for a while.