Survival endless breaks

As I played through survival endless it would sometimes slow down for a few seconds like as if it were in slow motion. At flag 125 the game broke entirely, All the animations stopped and the plants stopped functioning entirely. The zombies however, did not. Despite their animations being froze, them not spawning anymore, and randomly changing speeds, the zombies that were already on the lawn ate through my plants. I could do nothing but watch as the pause button wouldn't function either and eventually they made their way to the lawnmower. It went off but didn't effect the zombies as they continued on into the house ending my run. Luckily the death screen functioned fine and I could return to the menu with my high score even being saved, basically the game functioned fine after that.