How to know what is causing a weird lock screen with ads to show up? I have a Samsung Galaxy J7 that just started displaying this as the lock screen. Sometimes, it displays my regular lock screen, but if I let my phone sit long enough, it will display this screen. It always pops up, not just when my phone is charging. 

I don't know what it is, and the other questions I've found have suggested apps could be the culprit, but I don't have any of the problematic apps. I just want this thing gone, as it blocks my notifications.
Before downloading any third party app, do check if there is adds placed by devs.
Check if you installed any new app for lock your screen or for new wallpapers, these usually gives adds.


Most important: If you didn't find any of above case, then this is an internal app update which must be placed by company itself. Now you have to check every app by going to "Apps" section then "System apps" and look for any new app or apps related to wallpaper or lock screen and disable it.

Enjoy! It will surely work.