Screen Overlay Detected - Have read other threads and unable to solve

[AC Question]

When I try to enable permissions (for any app) I get an alert that says "Screen overlay detected - To change this permission setting, you first have to turn off the screen overlay from Settings > Apps.

To solve this issues I have:

1) Reset all screen overlay settings
2) Turned off "Draw over other apps" for all applications including system apps
3) Given some apps system permissions

None of these seem to do the trick. Anybody have any other solutions?

Specs;
HTC M10
Android version 6.0.1

This is starting to drive me crazy a bit as nothing on my phone (anything that needs permissions like attaching photos to SMS or update HTC) works any more.

Thanks!

Nish