I think the spotlight/contact bug was introduced in 11.1. It’s not fixed in 11.2.
If I search in spotlight for a Contact name, or search on Contacts field of phone app, I get an empty (Null) Contact as a result. It has no content.
Turning Search (spotlight) off then on for Contacts restores search, but only transiently. I have 2,162 Contact Cards, I did find one that was empty and deleted it.
I’ve now removed all Contacts from my phone (iCloud) and restored them. I’ll see if that works.