Just saw this on youtube. Problem is with the pen not the phone.
https://www.youtube.com/watch?v=IP_RIp3YIwk
https://www.youtube.com/watch?v=IP_RIp3YIwk
I had the same issue. Once I popped the pen out with a toothpick, I clicked the plunger for a few minutes. My guess is there is either a burr or the tolerances are very tight for the pen and it needs to be broken in. No, I'm not giving Samsung a pass on this.