Hello!
From my experience, it may be that too much coffee is ground that it simply does not fit in the portafilter. This can be regulated with the appropriate setting.
During the grinding process, you can briefly press the portafilter handle towards the machine, which puts the grinder on 'pause', then shake the portafilter a little so that the already ground coffee is distributed a little more evenly in the portafilter, then continue the grinding process by pressing it again.
Hope it helps.