In the past few months or so, I've had four confirmed instances of PMs not being received by the person I sent them to. One was to Gambit, one to Xylus, and two last week to Jordan. There's no sign that anything went wrong, I get directed to the inbox (or My Controls, I can't remember) as usual, but the other person simply doesn't get the message.
It may have happened more times without me knowing, and I haven't sent that many PMs recently, so it's happened a reasonably high percentage of the time.
Any idea what's wrong? Am I the only one?