Have you tried loading one bb into your magazine, then racking the bolt back again to fire? Since your gun is firing when the mag isn't in, maybe the hop-up unit is getting moved around by the mag.
Other than that, double check your airseal with your old hop-up to make sure it isn't some other part. Either way, you've convinced me to stay away from the Angel Custom hop-up unit >
Other than that, double check your airseal with your old hop-up to make sure it isn't some other part. Either way, you've convinced me to stay away from the Angel Custom hop-up unit >