I read a little bit more about this and managed to track down the issue. This bug - and a few other bugs relating to CSS sticky - will only occur if you have
Experimental Web Platform features
enabled in Chrome flags. This explains why only some people were getting it even though it’s the same version of Chrome.
If you’re seeing this issue. Make sure that it’s disabled here.
chrome://flags/#enable-experimental-web-platform-features
I sent a PR to revert the change above because it’s no longer necessary.