I also use bitdefender total security and after installing kb4571756 I can not boot to Windows stuck at the start screen with a few frozen dots, only option is to power cycle the pc.
This started the automatic repair where it gave me advanced options,attempting repairs over an hour.
I can also see that my usb 360 controller is not powering up,it failed to load after the update but also all of my usb devices are getting removed and reinstalled.
Things I have done, chkdsk c:/f/r/ DISM/Online/Cleanup-Image/RestoreHealth. Sfc,/scannow
Still can't boot properly
Win10pro 2004 amd 6x 800mhz to 3.3 ghz 8gb ddr3 usb xbox360 realtech hd audio creative x-if nvidia gtx 960 8gb vram
Legecy mbr bios c drive 2tb 2 3tb storage drives gpt format