I felt all your pain.
Mag kept falling out, either when the bolt catch was released or after the first round fired. Very disappointed but I did manage to get the scope sighted. Took it home and took a closer look. Even though it was making a good audible click the mag catch lever was not engaging all the way. I gave it a firm slap with the heel of my hand like you might do with a semi auto pistol and it caught, every time. Took it out to the field out back and a dozen or so bushy tailed ground rats paid the price of my success. Never a hiccup after that. Also ran a full mag at rapid fire too, no problem. I am happy.