This topic has not been resolved for me, I see it is a question posted by several others with the Verizon person making suggestions to turn off/on phone & update the app.
Both have been done for me and the problem persists. Also in addition to this problem, often 1 or 2 regular size pictures in a group of maybe 4 just load with a circle X and never show up in the text message....not ever. This is not related to my internet speed or system since it happens at a lot of places other than home.
The combination of these 2 very annoying problems makes me doubt the phone, Verizon or the app making me wonder if there is a more reliable message app out there I should switch to.