U can try another way to disable Intergrity checks through gpedit.msc . I know the commands still works in Windows 10 latest build , so it must have been some settings which are messed up in yr comp.
The Group Policy Object that you refer to only disables the Program Application Compatibility prompt while installing the driver. It does not prevent the drivers from being loaded once they are installed.
It is possible that the Insider builds allow for driver signature enforcement to be permanently disabled while the regular builds don't (or stopped allowing after some updated). I use Windows 10 version 1511 build 10586.