I have the exact same problem with a model 12FV in 223 and blind center feed magazine, but this issue first surfaced after a stock change. Now I'm thinking the magazine might be slightly out of place. First round pops up too far and gets jammed by the bolt as it moves forward.

Something else that just jumped to mind as I write this is perhaps I'm loading the bullet a bit too far out and the tip catches under the barrel as it comes out of the mag, or I'm not careful enough in loading the rounds and forcing them all the way towards the rear as I press them into the mag.