F**king SOLVED!!!! I’ve been having this issue on and off for years. After my upgrade to a new iPhone everything’s always fine. For a little while. And then inevitably one day I’m feeling nostalgic and search my text convos for that some random old image, and it’s showing me one of the following: attachment icon showing file icon and file name (IMG.***), attachment icon which reads “Tap to download,” or an attachment icon with a question Mark on it. It’s worth noting than none of these will lead to the image. Sometimes “Tap to download” does nothing, and sometimes it downloads and then levels up to a question mark. Every piece of advice I’ve ever recieved on this issue has had the same thing in common: WiFi. Connect to wifi. You MUST make sure you are plugged in and CONNECTED TO WIFI.
WELL. today it started working. When I was nowhere near wifi, but had cellular.
When I got home I plugged in my phone excited to continue, but it wasn’t working again. Cause I’m home now and it connected to my wifi.
i disconnect from the wifi, force quit (swipe up) messages, make sure I got cellular bars, and sure enough when I click “tap to download”, they actually do.
Hope this helps.
note: before any of this, first I toggled off and on Messages in iCloud under settings. A message will pop up, press continue, then try what I said above.