[Help] [Android] Source of Advertisement: Unknown

Hi Vergians,

I have a peculiar problem. I am getting full screen pop-up advertisements on apps or Launcher, and I do not have any idea what the source of the ad is.

I get these ads on apps which I have already bought (Pocketcast, Nova Launcher) or in Apps like Airdroid (which does not have such Ads). I am concerned about some shady adware apps. That said almost all apps are feom the Play-store.

Is there a way to know the source of this ad?

Attaching some Screenshots:

Screenshot 1: Airdroid

Screenshot 2: Pocketcasts