Try an uninstall of the current Piplay again but this time add these additional steps as well.
Delete the pvr folder if it exist.
Search for and open Device Manager.
Select "View" & choose to Show hidden devices.
Scroll down to Monitors section and right-click/uninstall all inactive monitors listed.
Reinstall Piplay and check again for the inactive monitors/uninstall them if present.
Make sure Extended mode works properly.
If not, Disconnect HDMI/Reconnect HDMI & turn the Pimax off/on.