Hi,
maybe you should incude fix mbr processes like this:
to your list of procedures?
For me it only worked to fix the UEFI boot as recommended here: (please be careful this is for advanced users and can cause serious problems with your machine) : https://neosmart.net/wiki/fix-uefi-boot/#Fix_1_Use
[watch out there seems to be an error in step 28: when it says "/s x:" I think the x: should be replaced with the letter of the system partition.]
Also I wonder if disabling the AV software is actually enough, or if it might help some people to disinstall them temporarily - including running the official removal software of the regarding AV company.
Finally I think there might be a point in recommending to turn on - also temporarily if preferred - Windows automatic error reporting and customer experience improvement program. To me it looked as if there were less errors in the setuperr file, after I did so...
Greets