contactsiosiphonemessages
This is recent (popped up in the last week), and I don't think it came up with any updates; most recent thing I can think of is watchOS 4.2. I'm on the iPhone 7, with iOS 11.2.
Only in my Messages app, some contact names are still visible, but most contact names have been replaced with their phone numbers. The contact "picture" on the side still has their initials though.
Any ideas on how to fix this?
It's an issue with OS X & Exchange sync. As a workaround, you can use the OWA app by Microsoft to sync your contacts to iCloud:
On iOS there's an app called OWA. Within the app there's a setting within the People section for sync'ing your contacts. Basically it creates a new group in your iCloud called OWA that is a carbon copy of your contacts.
Once I turned this on and saw it sync with my laptop, I got my names resolved and showing in iMessage again!
I have documented a more complete explanation and resolution in Resolving Contacts Sync on OS X - Error SOAPWebServicesErrorDomain.
On cause of numbers showing up instead of names is if there is a cached phone-number-only contact that needs to be removed.
Best Answer
I had this problem for weeks and tried numerous solutions like toggling on and off the short names, adding a country prefix to the number, etc. What finally worked for me was toggling OFF icloud contacts under Settings.