Channeling no matter what

Hello,

I have a Gaggia classic E24 model (15 bar) and recently bought a bottomless portafilter. No matter what I do, I get coffee or water spraying out of the bottom side of the portafilter.

I tried grinding finer, putting more coffee, putting less coffee, using WDT, grinding finer till the time to make an espresso increased over 1 min, using a puck screen, not using a puck screen. Same thing.

Coffee tastes delicious though, can't complain about it. I want to use the bottomless portafilter to have more space, but it can be a bit messy.

The only thing that worked was turning on the steam wand at the same time to reduce the pressure (by cutting a bit the flow of water). If I just turn it a bit on it works great and coffee tastes even better.

What should I do?