I've decided to roll back the Linux version of Kingdom Ka to the older engine. The main reason the game was ported was to solve a dpi issue in Windows 10 that the newer engine fixed. The user experience between engines is identical on Linux, as far as I can tell.
I'll continue to investigate the issues in the newer engine, but for now this rollback puts us in a much more reliable place for pure playability's sake.
If anyone is having any issues running this game on Linux, do continue to let me know and so I can commit time to investigating.