Lately I've received emails stating:
"xyz commented on your activity"
However, when I go to the activity it is blank. When I contact the sender they have indeed sent a message which I have never received. Is this a glitch of somekind?
Sometimes this happens to me too. I'm not sure what causes it. Sometimes what I do is then click to view my profile so I can see my full Activity, not just an email generated segment. That helps. If the conversation is happening on someone else's activity though, you'll need to go there instead.