Yeah, I had the same problem with my pups first bath last night.
First problem was just getting the spring back in there. I couldn't keep everything compressed while getting it in place, so the guide rod would back up into the cup, then would just jam inside it trying to recompress it while in place. I finally got the slide into the correct orientation that it went easy. If I can just remember how next time....
At that point I put the slide on the frame and the guide rod poked forward before the slide was properly seated. A quick look at the frame revealed a hole that the spring needed to enter on the frame. It was jamming on the edge. Lifted the edge of the rear of the spring slightly off the barrel and it went right together.