I'm not sure whether this is yet another iMessages bug, but it can be annoying when it happens. Here are my observations: -If you have an iDevice offline for a day or two, and use iMessages on another one, you will get all those messages on the offline device once you put it back online. Make sense. So far so good. -However.... if you restore from a backup to a new iDevice, that new iDevice won't receive all the messages that were "created" in the interim period (between the time of creation of the original backup and putting the newly restored device online). It just receives the new ones from then on. I suppose it's probably connected to the devices' hardware unique ID. Is there any way to force the new device to "re-download" missing messages?