It still locks surprisingly well. I can’t move it by hand when the trigger group is locked in place. But, it probably doesn’t hold tight enough when firing it. So, yeah that’s likely the issue. Can’t believe I missed that.Ohh yeah that lug is important.
How was the rifle even locking up without that? On one side only? That had to rattle.
When you get one make sure both lugs are round, so often they get out of round and don't lock up as good when worn.
What those two lugs do is "lock up" the stock, trigger group, into the receiver...
Without the lug.. problems to say the least.