Thanks so much! I really appreciate the kind words.
I think the bug might be your browser losing its WebGL context. Context lost events require games to rebuild everything because the graphics system on your computer has completely forgotten about the game (usually because it was too busy doing something else). They can be tracked, but it's painful to re-set-up everything exactly (ie, reload every texture, recompile every shader, etc etc) while the game model is still running; I've seen many commercial engines fail at this too. Since they're rare even when switching tabs, I didn't think it was worth tracking context-lost events too carefully in this jam but would definitely do so if I had more time. One reason why I recommend people full-screen the game is also as a signal to the graphics card that the game should take priority in video memory.
What you should still be able to do if it happens again, because it doesn't depend on WebGL at all, is hit escape to open the in-game menu. This should allow you to save the game, then refresh the page, and load your save. Sorry for the silly workaround!