This is 64 bit, and I'm using X, not wayland or mir. I thought maybe the error message would shed some light on the issue, esp the part about XInitThreads not being called, but if you use a framework that is not completely under your control, that might not help... but if you need anything else, like for me to run a debug build or something, just ask.
Yeah the thing causing the error message is Electron, however it's probable that the crash is due to my own misconfiguration. There's some stuff I needed to play with when hardware acceleration is/isn't involved that's sort of nebulous. It seems fairly reliable on Windows but I might just scrap that stuff entirely on Linux and just let people disable GPU manually via a command line option if they need to.