Mount fails with 'protocol driver not attached.' when Sophos Anti-Virus 9.5.1 for Linux is installed

With Sophos Anti-Virus 9.5.1 on Linux installed, an unexpected error occurs when attempting to mount a drive when the root device (The device mounted at /) is not of the /dev/hd[a-z] or /dev/ed[a-z]. format. To resolve the issue you will need to disable boot sector scanning on mount and un-mount.