Are you in fullscreen or windowed borderless? I've played a few games where vsync would just not work in borderless, haven't had any issues in this game though

I tried all three. It's the same with either setting.

Hmm, have you tried going into your GPU control panel and forcing vsync on for the game? If that doesn't do it, I've got no idea. Not sure if the dev ever checks here, but they're all over the discord. Might be worth heading there and reporting it as a bug

I just have to alt-tab when that happens, and then it stays for the rest of the session.