I put a Battle Arms mag release in an Anderson lower, and it dragged also.
Ether the slot on the lower for the left end of the mag release was a bit short, or the mag release was a bit long.
Hand sanded the end of the mag release by a few thousands of an inch, hit it with cold blue, and everything works fine now.
It's called fitting a firearm together, gun builders have been doing it for centuries...
Like Big Daddy Don Garlits once said:
"New parts don't always fit. You can buy more expensive parts, and they fit better, but you still have to check them, and many times make them fit also."