Coffee Biscuit doesn't come out in Knock Box We have a Breville Dual Boiler Coffee Machine, my husband even made a barista course to learn all about it. 
But when we try to knock the coffee biscuit into a knock box, it doesn't work. It never comes out and if you use more force, the filter pops out before the biscuit (hope it's clear what I mean). So you need to get a spoon and scrape the coffee out of the filter (and avoid doing a big mess). 

Does someone knows a trick or has an idea why it happens? I though, I use to much pressure to compact the coffee at the beginning, but according to my husband it's okay.
IF this is the machine you have, we're using the same.

Overdosing is the most likely cause. Please try to adjust the weight of your coffee dose.
We've found that 20-21 grams is still OK for the double-shot.