What happened to my contacts?

A

AC Question

I went to send an SMS to someone I frequently text and I noticed the conversation was missing. So I went to start a new conversation, when I typed their name, only their facebook info came up. I went into contacts and noticed they were missing. Now, I still have a large number of contacts, but a few are completely gone. Also, my "Recently contacted" contacts has a couple people I've almost never talked to, like a doctor I may have called twice a couple years ago.

Sadly, I don't back up contacts, I'm more concerned about why this is happening.

Running a Galaxy S6, recently upgraded to Nougat v7.0, going through Verizon.