I'm getting this same annoying "lockscreen" as well. Just started this morning. I'm on a T-Mobile Samsung Galaxy Note 4.
Every time I plug my phone in a charge or when I plug it out of the charger it appears.
I have already went through and tried seeing what apps were running to see which app was the culprit. I have already uninstall many apps which I thought was the offender to no avail.
I have attached screenshots of the offending slide to unlock screen. Can anybody confirm that it resembles what is showing up on your devices? I don't know what this is but it is super annoying. Probably not a coincidence that a security bug is affecting many of us users as this thread was posted today and I started getting this today aswell.

