I have an iPhone 6S. On both mine and my Wife's phone the text messages are appearing out of order. This has been going on for the past year or so and is typically when a text is responded to within a few seconds. For example, I send her a text and her reply would show up above my sent message. If I don't scroll up I would not see her reply.
From the research I have done this appears to be a fairly widespread issue and I have not found a remedy for it. More of a nuisance than anything else, but I would love to find a fix for it. Phone is running 11.2.5 software.