I was running my LSS on Monday with their .223 mags. I had noticed they fit a bit loose in the LSS before heading to the range. I didn't think much about it. Tried running it at home with the 1 snap cap I have with no problems.
Previously I had been using the .223 mags in an HS stock that I'd installed a Magpul dbm kit into. This setup ran flawlessly and the mags were nice and snug.
Once I loaded 10 rds into the mag at the range, the loose lss magwell caused either a jam or a failure to strip a round from the mag. Once I realized what was happening and began applying slight upward pressure on the front of the mag while cycling the bolt I had no more problems. Still a pain in the butt.
I contacted MDT and had a reply first thing the next day. They were excellent quick to deal with. They offered to send me a set of different mag latches to hopefully hold the mag in the proper position.
I don't know if this is the same problem, but so far MDT have been wonderful. Especially since I even told them the chassis was a second hand purchase.