iMessage attachments disappeared with iPhone 12 Pro

I just updated to iPhone 12 Pro and when I set up the phone from an iCloud backup, my message attachments disappeared. They are present in the conversation if you scroll up through the thread, but not in the attachments screen. In my iCloud storage, the storage amounts are indicative that the attachments are still there. In my iPhone storage, the amount is much lower, but I still get the “remove large attachments” suggestion to save space on my iPhone, and then I am able to see large attachments in that screen. How can I save 21 GB if it thinks my total messages are only 2.7 GB? I just want my attachments back - help!