This is very good advice! Most gunsmith's know nothing about AR's and as a certified armorer myself, I've fixed quite a few including some "custom" builds by "reputable" gunsmiths.

Jay,
please clarify if the issue you're having is feed only or is it also a failure to extract/eject as your video seemed to show? Feed issues could be isolated to magazines, but the other stuff is most certainly gas related. If the gas block is good, then move to the tube. Is it aligned/installed properly? The roll pin is in-place holding it in the gas block, right? Oriented properly? If all that is good, move back to the bolt carrier. Are the gas key screws still tight/staked? If so, move to the gas rings, make sure you encounter resistance when pushing the bolt into the carrier...this is the spring action of the gas rings closing and sealing. If all of that works (can't imagine it will based on the malfunctions you're showing) then I'd send it back to Smith.