OP, have you read the app's FAQ/tutorial? I also haven't used it in a while, but I remember the dev stating that there was a delay, at the OS level, that meant when you powered your screen off, you had to wait a little while for W.L. to be enabled (unless you rooted, at which point you could authorize W.L. to bypass that). Are you finding that the old lockscreen comes up if you turn the screen on right after having turned it off? Or do you see it after its been off for a while?
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