Acceptable ad setting keeps changing

[Topremodeler]

I set the acceptable ads setting to "block all advertising" and it works for a while. Then I start seeing "acceptable ads". When I check the setting, it has been changed all by itself. I reset it to "block all advertising". Several hours later, it will have switched itself back. I have scanned the phone with Avast and it scans clean. There are no other signs of malware. Any ideas of what to do?