Best bet would be to try a different magazine and see if that fixes it. Thermolds are about the least expensive magazine on the market, which would make me suspect the $5 magazine rather than the $1000 rifle. Make sure the rounds are in the magazine properly, not pushed too far forward, insert the magazine into the mag well, whack it fairly hard on the bottom of the mag to make sure it is seated, pull back the charging handle all the way, and let go. Do not try to ease a round into the chamber, it won't work with an AR. You might also inspect the feed lips of the magazine to make sure there is not a mold flaw or something else making the rounds hang up.
If you don't have another magazine, find someone else with one and borrow it to test.