A second lock screen suddenly appeared earlier today, how do I get rid of it?

[Android Central Question]

The lockscreen contained ads. I have a Samsung GalaxyNote8. It had a drop down option in the corner, so I was able to disable it earlier, but it just came back. It also had two different pictures both times. I've been trying to look up where it came from, and everyone says it's likely from any recently downloaded apps, but I haven't downloaded any recently? I've been going through my phone trying to delete any recent files, but I'm still worried whatever caused it is still there. Should I reset my phone?

 

[methodman89]

Place the phone in safe mode to verify its a installed 3rd party app.