I have a number of SD-cards, with Windows IoT Core installed, which has been running in Raspberry Pi 3b for a time, sometimes weeks and sometimes months. They all have some kind of boot issue. Some wont boot at all, I can't even reach the Windows Debug Portal, so I assume that the installation of Windows IoT Core are totally broken. Some boot fine most of the time and sometimes fails with an error 
which reboots after a couple of seconds and often times manage to boot properly.
I have tried to follow this guide: https://learn.microsoft.com/en-us/windows/iot-core/manage-your-device/windowsdebugger#raspberry-pi-2-or-3-rpi2-or-rpi3 but when I try to run:
bcdedit /store c:\EFIESP\EFI\Microsoft\Boot\BCD -debug on
I get: An error occurred while attempting to access the specified entry. The system cannot find the file specified..
Blue Screens are also pretty common, when they happen the system does not reboot as far as I have seen.
I know that the devices are fine and working, and the SD-cards also seems to be fine, no broken partitions or similar.
How do I find out what went wrong?