One of these things worked for me:
1) turn icloud messages off then back on
2) go to settings/siri/messages and turn everything off, restart phone, turn everything back on
3) did an icloud back up
Not sure which one did the trick but all my attachments/links/search is now there.
so I turned off everything in settings//Siri messages. Rebooted and went back into settings/siri and they were all on automatically. A bug? Anyways my search still doesn’t work in messages.