Is it hitting on the slide stop which is sometimes hard to push past or gets close and just won't quite latch up?
I'd lock the slide back and then seat the mag, that should make it very easy. I often time push the mag release button as I insert the mag so it gets past the catch with little effort and to me just saves wear and tear.
You might also load a round (if you haven't already) in the mag as you load the mag, that might help.
They do some times require a pretty good push to seat.
Keep playing, we'll figure it out. Glad you found us.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."