Downloading attachments in iMessages (problem)

I have a new iPhone 17 Pro with the latest iOS 26. There is an older iMessage that is a few months old that I am active on again, with a friend. I want to download the attachments.

Unfortunately, when I go to do this, I see "Downloading 46 Attachments..." and it eventually resets. There is nothing wrong with my network (which is very fast), everything else is working just fine. I checked that iMessages are being synced in iCloud (that is my preference) -- restarted this a number of times and I've given up.

Am I running into a new bug? How else is this supposed to work properly?