We would highly recommend reaching out to Radical Firearms or techsales@opticsplanet.com with more details regarding exactly how your rifle is set up and what kind of ammo you are shooting because the cause could be a wide variety of issues that will have slightly different solutions.
What buffer tube do you have in it. That could be the issue, if it is to soft then it does not have enough pressure to eject casing.
Are you using subsonic ammo? That won’t cycle in my gun without a suppressor. Try shooting some 110gr supersonic ammo. That should work