Shape builder tool not working

Hey! I know this is like a very old thread but I was having a similar problem and no answer here helped me. However, for me, the reason why the shape builder tool wasn't working was that I had a mask active on my shapes (EVEN THOUGH IT WAS TURNED OFF, I HADN'T 'RELEASED' OR DELETED THE MASK). Releasing the masks (after deleting everything from the mask layer) solved the problem and I was able to use the shape builder tool as usual. So this is one of the things you might wanna check