RESOLU: Voici une réponse qui résout le problème. Je l'ai posté en anglais sur le forum Apple.
Ca a marché pour moi. J'ai probablement forcé la re-indexation.
Le principe est de désactiver la recherche Siri de Messages et de la réactiver.
Yeah!
"Hi,
switching to iOS 11 from a 6s backup to a brand-new 8+(iOS11already installed) I had the same problem.
It has been at least my 5th upgrade/swith/change of iPhone and never encountered this issue before.
But I think I FOUND THE ANSWER . Note that I used it on my French language/French hardware iPhone.
1) settings->siri and search
2) de-activate Messages search
3)shut down the iphone
4) Reboot . Don't use the messages app
5) settings->siri and search
6) Activate Messages search
7) Wait (I know it's hard) at least a minute
8) Go to Message App. Should work. "
David
