I don't think it's the Meijer app causing the ads. I just recently got this phone so it's my first android phone in a while (I was using iphones before). There was an icon set that I really liked back when I had my last android phone (Note 5), but they are not available on google play anymore. So I did some googling and I found them online. They were available as APK files and so I downloaded them and have been using them on this phone. I'm just wondering if those are the things causing these pop up ads.
That Meijer app is the only non-preinstalled app included in your "Last Used" list in the Play Store and the screenshot is named after it. If you prefer you can run a few more test, including restarting your phone, waiting until the ads popup and then check that Play Store tab again. I'd say that you are going to find the same results.
Those full screen ads don't popup right after installing the app, they have some internal switch that is triggered after a certain amount of time, after the app gets updated or even after you get a system update. There's not a single rule.
If you want to be 100% sure I'd recommend you to kill that app with fire (see my guide for instructions) and then see if the ads come back or not. Or just keep the app and search for another culprit.
Tell us how it goes.