I don't know if this will work on an iPhone, but I figured out how to get the contact pictures to show up from my Galaxy S7 edge. I tried playing around one day to get the contact images to show up after, like you, one contact picture mysteriously showed up. I thought it must have been the file size or type of picture my ex-gf had taken and sent me, so I tried a bunch of file sizes and formats... with no success. I even tried importing the contact list in the head unit to no avail. When a *second* contact picture started appearing whenever my friend would text me, I was able to figure out what was happening. This allowed me to think about what these 2 contacts had done which was different than all my others. And the answer was...Yesterday, one contact picture mysteriously appeared and continues to appear properly. This happened after I updated software on iPhone 6S to 11.1.2. However other contact pictures are not showing up. Any thoughts?? I did nothing intentionally to make it appear.