It hasn't popped up since I deleted mapgenie for the division 2,
Mapgenie for red dead redemption 2,and Craigslist pro (free version)
Also cleaned my browser cashes.
I don't think it was in a app though unless its time delayed malware because I didn't Install anything new in 98 days and it just started popping up last week.
Keep us posted, if the symptoms persist!
So in my experience I had the same problem and I found a solution acting as described on my web site. I apologize if I can't translate the article but I have no time at all. However it can be useful to someone and I leave you the google link with already the automatic translation.
In particular I found a workaround to the problem waiting to solve it which was very useful and which put the malware in a golden cage without access. In the article I described how to change the default program as a browser and then disable it so that the malware becomes harmless trying to open a page of an inactive browser. Then I solved with a double cleanup of the system as I described on the post. Greetings to all.
You can find my post searching on google.it "Come bloccare PopUp e Pagine Web di Siti Internet che si aprono da sole su Android" ( analisideirischinformatici.it )