Trouble with text monitoring

Norton Family is monitoring my sons text messages. Up until a couple of weeks ago I was able to see who he was receiving and sending texts to plus dates and times. Now I can still see and read all but one person's texts (sent and received). I can still see the person's name, date and time, but not the actual text messages. Nothing, that I'm aware of has changed. It's happened before, a few months ago, but corrected after a few days (not sure how).