Hello vomorenburg!
Here are some steps that seem to solve this issue:
- Force restart iPhone - Apple Support
- Please ensure that iCould Photos are turned on: Set up and use iCloud Photos - Apple Support. After turning on iCould Photos, go to the contact in Messages, click on their contact pic., then scroll to the bottom, and see if you see a message along the lines of: “(number) of images available to download from iCloud.” Click on “Download,” and the photos should start appearing as they download.
- I was asked to troubleshoot this issue on a relative’s iPhone. iCould Photos were turned on, but his iCould storage was full. So I used this Support Article to “make some space,” and the photos started showing correctly.
Also…
- Please turn off your iPhone. Leave it off for 5 mins.
- Please turn off iMessages in your settings.
- Turn off iPhone.
- Leave for 1 min.
- Turn iPhone back on.
- Go to Settings, and turn iMessages back on (wait 1 min. after doing so)
- Tap on JPEG files in your messages, and they will appear (some automatically)
Please report back on wether performing these steps solved the issue, or if they did not solve this issue.
I hope this is helpful. Good Luck!