Mobile Security - App Store Opening

Re: Fully protected mobile device (S6) unprompted opening of app store to unknown applications for download.

So at random intervals when my messages or whats app is opened, Google play opens to random apps such as games, online gambling, etc. I’ve ran several scans isolating network connections to try and detect malware, viruses, etc to no avail. Anyone aware if boot scans can be completed through Avast! on Android OS? Or if there’s a defenition update coming out to detect this?

Factory reset phone and dont download crap …