failed to enroll MOK key on upgrade 17.10 -> 18.04

I upgraded my development edition Dell XPS 13 9360 (i.e. single-boot Ubuntu) from 17.10 to 18.04. During installation, I was asked whether I wanted to create a MOK key to install third-party drivers under secure boot. I said yes and specified a password. After restarting, I was met by the MOK management menu, with four options (iirc):

1. continue boot
2. change secure boot state
3. enroll key from disk
4. enroll hash from disk

I chose 3. However, it didn't accept my password, so all I could do was to proceed with 1.

The upgrade completed without issues, but in order to decide for myself whether this is a problem, I want to better understand the situation.

Specifically, I would like to know:

1. Was enroll key from disk the correct option?
2. Why was my password rejected? Could it be the MOK management menu uses a different keyboard layout from my standard layout in Ubuntu?
3. Does this mean certain third-party drivers were not installed? How do I know which drivers, and how do I get a 'second chance', so to speak?
4. mokutil --sb-state says SecureBoot is enabled, but I seem to get a message saying secure boot is disabled at least sometimes on startup. Perhaps only when I reboot? Is this significant?
5. Do I even need third party drivers on this system? The only components that I feel could work better are the wifi, the touchpad (palm sensitivity when typing) and audio quality with plugged in earphones.