intermittent ctrl keys on matebook X

[yuzuuser]

Just installed xubuntu 18.04 on a huawei matebook X with a japanese keyboard.
After the initial install everything looked great, but after powering on the next day i noticed that the control keys weren't working (do not show up in xev or showkey) ... funny, i'm sure they worked last night...
There's a lot of "control key not working" forum content to get through (mostly keyboard shortcut related), but none of it worked for me (gnome-tweak-tool included). Apologies if i somehow missed the killer thread.

After scratching my head a few hours i noticed that they started showing flickers of life ... working intermittently ... few hours more, the battey is running down so i connect the power - then they're suddely working 100%.

Have now repeated several times and as far as i can see it's like this:

• from power on with battery only : ctrl keys not working
• on battery, after a little use (crazy ctrl-c'ing in terminal window) : start working intermittently, but not to a useable degree
• with power connected : work 100%
• behaviour is exactly the same for L/R ctrl keys. No other keys have problems

Unfortunately this was a new laptop and i deleted windows so i have no evidence that it's not a h/w fault, but i don't see how a hardware fault would affect only, and both ctrl keys.

Any ideas?

[VMC]

"Settings > Hardware > Keyboard"
What does your keyboard layout show?

[yuzuuser]

Thanks for responding.
Currently it is set to Japanese (kana 86), the model, customization and compose key options are all unset (menus show "-").
I have tried a couple of the other japanese layouts too but didn't notice any difference in behaviour. To be honest i don't know what the most correct setting is here.

UPDATE: kana-86 is the correct setting, but this is irrelevant to the problem.

[yuzuuser]

... after that, i accepted some auto-updates, and then the ctrl keys stopped working alltogether ... have now given up and arrived at a useable environment via a bunch of xmodmaps.

I guess this is a matebook issue, rather than any shortcut/keyboard mapping thing (as discussed elsewhere, media keys also don't work on matebook linux). Would still be interested to hear from anyone who has a properly working matebook X with JP keyboard, or who has seen this seemingly power-related intermittent behaviour.