If you have a game that uses Unity Engine like Immortal Redneck or Sundered, just to name 2 examples, and use multiple keyboards layouts in KDE5 ( not tested on other Desktop Environments ), you probably have noticed that the spacebar sometimes doesn’t work.
For mysterious reason, if you start the game with the secondary keyboard layout it doesn’t reconize some keys, so the fix is simple and somewhat effective, but you don’t find much information on the interwebs if you don’t know exactly what you are looking for, just change to the default keyboard layout before starting the game and voila.
Sources:
https://steamcommunity.com/app/510490/discussions/0/1694922980039139214/
https://bbs.archlinux.org/viewtopic.php?id=233050