I purchased the blind rivet one but haven't had much luck with it. I've tried using it a couple of times but it won't eject the rivet needle.
If this happens in the very first few rivets sets, grease in the adapter can be stopping the stem from falling out from gravity and tapping the side of the adapter against a surface can remove it.
Make sure the nosepiece and front tube/bushing are screwed all the way down.
If it keeps happening, check the length of the rivet body is not longer than the tool can set. Or use the next nose-piece size up if not already setting max size.
Some people setting aluminum rivets see this issue as rivet material builds up to gunk up the nose-peice exit. Traditional rivets fall out the back so dont mind it, but these having to expel out the front get stopped by any soft material left around the nose-piece hole.
A test you could do to see if it's actually jammed our just not falling out from gravity (all stems look jammed once you take the nosepiece off as the jaws will sinch it), you could set a rivet with the flange not flat against the nosepiece, leave a 1/16"-1/8" gap or so. That way when setting the rivet and returning the stem forward, you'll have enough exposed out of the tool to grab with your hands. If it comes out easy when exposed, some grease is likely gunking it up.