I have an iPhone 7 which was synced perfectly to my car till not long ago when the contact list just vanished. The phone is connected with bluetooth just fine.
I can't find a sync button or any other way to fix it.
I had the same after current iPhone update. Two things to check. Make sure you have current hardware updates and make sure that in iPhone settings/ contacts/ default account/ you have the account where all contacts are contained. In my case Gmail. After update it had defaulted to iCloud.