My wife and I both have Iphone 8 running 11.4 (or at least mine is 11.4)
Very weird behavior that I noticed happened recently. I usually set my Airdrop to "Contacts Only" and leave it as such. I remember being able to send/receive photos or videos between our phones in the past using Airdrop.
However, yesterday, I had to set my Airdrop to "Everyone" so her phone could see my phone to send photos/videos. Why did the behavior change? She is a contact in my contact list. I even tested to make sure when I called, my contact name/photo pops up and vice versa.