Tried Safe mode, PRAM reset What worked for me: Boot into Recovery Start Security Startup Security Utility and set Medium Security. See https://support.apple.com/en-us/HT208198 Reboot and upgrade. Go back and set High Security (if required)

Same problem for me. I also had the problem with 11.2. Tried in safe mode, no "luck". Some "suggests" that resetting NVM can fix it. Other says the "solution" is to do a reinstall. But these is work-arounds and not fixes. Apple, Wake up and fix your update process. At least acknowledge the issue!