For some reason, Caps Lock stopped working on my machine. Not only on the laptop keyboard, but on any connected keyboard as well. I'm using 18.04 on a Dell XPS 15 9560.
It worked perfectly until a few days ago and it stopped working after rebooting when I just had done a regular system update.
Had similar problems with a KDE VM that had been working for years, before a VMWare update, and after trying MANY possibilities within KDE, to no avail, turned off the VMWare's enhanced keyboard and everything returned to normal.