Ubuntu – Keyboard specific keys stopped working (Sound BlasterX Vanguard K08)

keyboardkeyboard-layout

I'm using a Sound BlasterX Vanguard K08 keyboard, which features a couple extra keys (five macro keys, some media keys and a volume rocker). My OS is Ubuntu 19.10 (eoan).
It used to work fine for a couple days since the install, but since today or yesterday, almost all extra keys have stopped working:

  • Two of the five macro keys still work, three don't. The ones who don't work anymore are bound to mouse functions, btw: Left-, right- and middle click. Haven't yet tried to switch them around.
  • The media keys and volume rocker don't work anymore.

showkey does not register any input for the keys that aren't working anymore.
Not really sure what I changed. It possibly coincides with installing dconf-editor, but I only used that to make monitor-setup-related changes, nothing related to the keyboard.

I do not expect to be able to setup the macro keys in Ubuntu, as I can do that under Windows. When booting into Windows, btw, all keys still work just fine, so it's not a hardware issue.

I looked at the following, somewhat similar problems (and others, which are analogous to the ones below):

Media keys not registered: Similar, but doesn't have an answer yet.

Media play/pause & track prev/next stopped working after reboot: Solution didn't work for me, no change after applying the settings.

Media Keys not working on Ubuntu 17.10: Doesn't apply, showkey doesn't register input in my case.

External article "How to fix media keys not working on Linux": talks about playerctl, which wasn't necessary before and wouldn't solve the issue with macro keys.