I have an iPhone 8+ and I've always had problems with sometimes not receiving calls for 1-2 days after someone called me. That's not often but it's happened, and texts sometimes don't appear for a couple hours after they were sent to me.
Also been having a problem the past 2 or 3 weeks with slow internet connection, or none at all. My data sometimes doesn't even work. But everybody else in my house has no problems.
What could be the deal? I've restarted the router, my phone, and no change.
Read more: https://iphoneus.org/faq/iphone-8-doesn-t-receive-calls-right-away-and-problems.html