I've been using an IMS shower screen for a while now without issue, shots looked beautiful and tasted superb. Recently however, I started getting sour shots from the result of bad channelling. Tried altering my technique, decreasing/increasing dose, lighter tamp, and experimented with WDT to no success. Just donut shot after donut shot.

Upon cleaning the machine I noticed a 'pop' sound and decided to remove the shower screen to inspect further. I discovered the membrane of the screen was actually moving in and out, kind of like the safety button on the lid of a jar. My theory is that when the water hits the puck and grinds expand, it's pushing the screen up and clogging some of the finer holes in the IMS. What originally caused it though, is still a bit of a mystery to me. The baskets (to my knowledge) have never been overdosed to the point that this should have occurred.

The screen unfortunately now seems ruined. Even after making sure the membrane is where it should be and reinserting it, channelling continues. I have since gone back to using the stock shower screen and enjoying nice shots once again.

Has anyone else encountered this with the IMS screens before?