Sure! Here's what happened: after I bought all the upgrades, I started a new run. I had full health (5 hearts), and I noticed that when I collided with enemies, they just didn’t deal any damage, no matter how many times I tried. None of them did. The issue continued in the following runs as well. I'm not sure if it’s related to the upgrades or something else, but I probably did something that unintentionally broke the game.