The puck is getting compressed too much so that the water cannot flow through. The puck screen takes space and is not allowing the puck to expand.
Use a deeper basket and do the same - you’ll see the shot will flow normally again.
The puck screen doesn’t restrict the flow as such. What restricts the flow is because there’s no headspace for the puck to expand.
Put a £1 coin on top of the tamped puck, lock the PF, remove it, and then check if there’s an indentation. If there isn’t, then it’s good. Now put a 10p coin on top. If you get an indentation, then you need to lower your dose as the 10p coin is thickness of the puck screen… actually slightly thinner.