For anyone who still have that issue and googled this topic, I had similar problem and solved it by running Rimworld with apulse. Not 100% if that is something to do with actual pulseaudio since same Rimworld runs fine w/o apulse on my other machine with virtually identical Gentoo Linux and the only difference I found is that machine that runs it w/o apulse has single ALSA sound card and machine where Rimworld crashes has two.