Welcome to the forum. Big surprise! a BT .380 that hangs up?
Sounds like you have done the standard stuff without any physical mods to the gun or mag. Shooter's question on the bullet type FMJ or HP would be my next question?
If it does the same with both, a few things to check next. That is assuming you want to risk voiding your warranty cause it is a new gun. If it was used I would suggest the following:
If you are in a safe location, manually cycle the gun with every round to see if it hangs up. Inspect the round that hangs up. Look to see if the rear of teh cartridge has cleared the mag lips. You might check this while firing it and insepect when it hangs up. Looks to see if the round is still partially in the mag or if it is clear of the mag and hangs up on the breach face, extractor, or fining pin hole area. Inspect the round and visually inspect it for scratches or rough marks along the rim of the case. If it is not safe to do so, skip it.
See if you can locate the trouble spot. If the rear end of the cartridge is hanging up on any of those areas, a light polishing would be in order. Just have to know what you are doing or you will damage harded steel parts. If it is a mag issue, changing the feed lips to change the feed angle of the round may help. ...or make it worse. Kinda sounds like the feed angle is a bit wrong or the round is not clearing the mag lips completely and is going in the chamber at the wrong angle or binding. Just trial and error mostly.
Also remove the slide and put it back on without the spring or mag. Work it back and forth and check for binding. Probably not that cause the rest of the rounds feed o.k.
And most people will tell ya it just needs a "break in" period. Maybe, but it should work right out of the box. I only buy used guns and have to tinker with them when they don't wprk cause there is no warranty. If ya can't diagnose it quickly and it is under warranty, a trip back to the mother ship would probably be the best thing. I have had several of the .380s. All used, all fed correctly. Never even cleaned any of them when I got them.