I have the same issue. Maybe it’s related to WiFi. I tested the PIR with on older PI 2, no WiFi. Ran the Python script, working perfectly.
After installing the PIR to my Mirror Pi, a Pi 3 screen wouldn’t go out. Installed the test Python script again and I am getting a lot of false positives, over 5 a minute. So PIR stays highs and screen stays on.
I am thinking that WiFi is interfering with the PIR.
Anybody any experiences or ideas?

Thanks,
Herman