It might depend on how long you play, what other tabs are open, what extensions are active, what order things happen in the game. It could be that some change in Chrome made the issue more obvious now for some reason, or something else on your computer changed.
pretty much every time I have looked into an issue like this, it was because I (or someone else) forgot to destroy explosion instances, or millions of bullets were flying off to infinity, or particle instances were adding up, or some condition was true that continuously spawned an object, and the increased number of objects was bogging down collision checks, etc...