@kbz1960 is right... it's probably related to an app you've recently installed. Go through your list and uninstall apps from the most recent and keep going until the second lockscreen disappears.
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I'm having the same issue. It just recently happened after I just installed the latest security update for my phone. Prior to the update it was not doing this. I will try to post a screen shot of the update notes. Any help would be very appreciative as this is extremely annoying.
Did you ever figure out how to get rid of this second lock screen with the ads? I recently got it on my phone and it's so annoying, I have no idea how to get rid of it