This last month I have had numerous problems with my iPhone, not being sure messages that say they are delivered are actually delivered (recipient said was not and has caused lots of stress on my end). To top it off, recently sent a pic on iMessage, the recipient responded by talking about the pic, then later it said not delivered. This has happened with other Christmas pics I sent same person. The pics say delivered, are commented on, then later say not delivered. What does this mean?