I'll join a Coop match, play about 30-40 seconds and then I get kicked from the game with a popup from EAC. The Alpha ran just fine before. My anti-virus is just Windows Defender.
Could you please be more specific ?
I had this happen to me after the game crashed and I let it restart from the Unreal Engine crash window. Restarting the game properly fixed it. Is this perhaps what happened to you?