At some point my Windows (Super) key stopped working. 

Trying the following doesn't produce any output when the super key is pressed:

$ xinput list
WARNING: running xinput against an Xwayland server. See the xinput man page for details.
⎡ Virtual core pointer                     id=2 [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer               id=4 [slave  pointer  (2)]
⎜   ↳ xwayland-pointer:18                     id=6 [slave  pointer  (2)]
⎜   ↳ xwayland-relative-pointer:18             id=7 [slave  pointer  (2)]
⎣ Virtual core keyboard                   id=3 [master keyboard (2)]
    ↳ Virtual core XTEST keyboard             id=5 [slave  keyboard (3)]
    ↳ xwayland-keyboard:18                     id=8 [slave  keyboard (3)]
$ xinput test 8


But pluggin my keyboard into my work laptop running windows it works fine.

Thanks,
Richard