This is very strange but I hope readers can follow. My phone is an iPhone SE running iOS 11.2.6, mac is a 2011 iMac running macOS Sierra (10.12.6), iPad Mini 2 is on iOS 10.3.4.
I often send myself messages on my various device, as a quick & dirty way to copy text from one to another, i.e. phone to iMac or iPad, or any other variation on that theme. Normally when I do this, I see the sent message in grey on all devices, and the received message immediately after in blue. Makes perfect sense since they are all logged in to the same iCloud account.
Recently however, something has changed. When I sent a message to myself on any device, it works as normal on my iMac, Macbook, and iPads. However on my iPhone, I see TWO chats with myself. One gets the grey message (indicating what was sent) and the other gets the blue message (indicating what was received).
What the heck is going on here? Both chat threads are with the same contact (mine), and I see no difference between them at all. I have tried deleting one of the conversations, but it just gets recreated again.
All my devices are set in Messages preferences to use my email address for all new conversations, and I'm set to be reachable at my phone number and email address on all devices as well. I'm stumped.