Did you run MB device manager as Administrator? If not, then you will get the "Failed opening Com Port db, err code 5" as well as an incomplete log file.
The drivers you have are not too old, but something might have corrupted them. You could try this step from the FAQ page with all Microbit devices unplugged:
Uninstall all Microbit ports/devices. Answer ‘U’ on the question ‘Do you want to uninstall all Microbit devices automatically?’ followed by ‘C’ to do that. It is advised to unplug all Microbit devices before uninstalling all Microbit devices
Then reinstall RRC Micro, which will reinstall the Com port drivers.
If that does not help then I really would need the complete MB device manager log file, which should be created if it's executed as Administrator.