This is known issue and Apple is working on a solution. To ensure Apple knows you too are having this issue, provide feedback via this link directly to them: Feedback - iPhone - Apple
My iPhone 7 Plus has a bad habit of displaying text messages in the normal iPhone text app in the wrong order. I can send a text message and 5 minutes later, the response from that person appears above my previous message as if they had responded to that particular message before I even sent it. IOS Version 11.2.5
2 replies
I would restart my phone or even maybe try to update it if it's not updated to the latest feature.
iPhone 7 Plus displaying text messages in wrong order