Oh my -this has been driving me crazy for 3 days, and I'm out of town and the "screen overlay detected" pop up was making Waze and Audible inoperable!! Tried all the relevant suggestions (I have a Samsung S6) - changing the settings in Applications turning off the overlay for all apps didn't help, Don't have any of the Cheetah Mobile apps complained of above, etc. etc.
Finally noticed a mention of turning off auto brightness. So I did. I also realized that ES Task Manager persisted in offering its quick access function (swiping from the corner gives you access to a customized quick menu of apps -- AND IT IS AN OVERLAY) even when it had been denied pop-up permissions. So I deleted ES Task Manager.
Rebooted. Phone seems fine! I'll do a little more experimenting to see which is the culprit (voting for ES Task Manager, which I only implemented a few days ago).