I don't recall exactly when this started happening. But it's becoming worse and getting really frustrating over the last couple weeks. When texting friends and co-workers from my Pixel 2 XL, the messages i send are out of order.
Today i sent 3 messages to a friend of mine who is on AT&T with their default Samsung 7 message app. The 3 messages i sent over a 15 minute timespan were all grouped together, showing the same timestamp, even though i sent the first, got her reply, then sent the 2nd and so on. This also happens to my son on his iPhone 8 with Verizon's Message +. His messages to me and mine to him are out of order, and it's just random when it does this. I can message all morning and have them send just fine, then maybe at lunch, or after work, or in the evening they might show out of order. Nothing i can pin down to say "that's it!".
It's odd it's happening on both iPhone and Android, and across carriers. that definitely points at a problem with the message + app. I've just switched my messaging app to the default messaging app on the Pixel 2 XL, and so far haven't had any issues with out of order messages. However it's so random that i won't be sure for at least a day, as it's happing at least once a day now. The only thing i can think of that may be a factor is my phone is on a business plan with my company while my son's and friends' phones are on personal accounts.
My app and my son's app, and hopefully my friend's message + apps are all up to date, version 6.6.5.
I have cleared cache and data in the app.
I have uninstalled, cleared phone cache, rebooted and reinstalled the app.
I have done a factory reset on the phone, clearing all apps and all data.
I have setup the phone (after the reset) as a new phone (no backup restoration).
So far nothing has worked.