If if you power off phone standby mode and turn the phone back on, it usually shows this ad and displays something about memory status or battery status and has an ad below. I want it gone I don't know what's causing it iuninstalled many programs and even tried ad blockers and virus scans...
Welcome to the forums. What happens if you tap the three dots on that pop-up? It's probably caused by an app that you downloaded, see if this guide can help you to find the culprit.