DrForinor - if it’s the Elizabeth…. It’s only held in place by…. Nothing!
The only reasonable explanation is some dry coffee “cementing” it there. 2.5 years with the Lizzy and this never happened to me, and I don’t remove the dispersion screen very often at all! At the beginning I did, but always found it was very clean. Then I started leaving for a month, and then two… and no difference. In any case, every two months I take the group apart, give it a good scrub and put it back.
So tap-tap as Dave says is all you need to do. Or try rotating it with your hand/fingers.