How much lube are you using on the bolt carrier gorup?

What type of lube are you using?

What temperature is it where your shooting?

What type of ammo are you using?

Is the action clean?

Does the bolt catch look normal? Any noticeable wear?

Does the bolt catch operate freely?

Does your magazine follower operate freely? With an empty mag, pull the follower down, than slowly let it back up. Does it return all the way up every time?

Any of these things could contribute to the problem.