I have had this issue for the last year and a half. The issue has followed me through three iPhone 6 Pluses and now an iPhone 8 Plus. Started somewhere in IOS version 10 something. Symptoms are:
1. Open up messages and no messages show up, only blank spaces separated by lines where messages should be.
2. Severe freezing of message typing and message output. Typing delayed by 10-15 seconds, rapid catch up, then delayed again. When message attempts to send, the bar goes across 3/4 of the top of the message and then stops and freezes.
Solutions I have tried:
1. Turn phone on and off. Worked well initially but got worse with each new iOS update.
2. Hard restart of phone - same results.
3. Checking memory and reducing retention of messages from forever to 30 days (this one sucked because I gave up many old messages.
4. Killing and reopening message app. Didn't work until phone was shut off.
5. Killing all open apps. No effect
This is extremely frustrating. It's amazing to me that Apple hasn't updated the issue or even responded. I think it's a result of the clocking of older phones and the programming stuck with each new update like a ghost. Now Apple is getting sued. I might join.
Gonna lose a customer Apple if you don't get it together ASAP