SMS (green) message read status not syncing from iPhone

Found a solution for any other random person searching in frustration for a solution, compliments of a Reddit user. His fix is related to an Apple Watch issue, but it also solved my issue. Here it is:

Just wanted to report back on something that fixed the issue for both my gf and I.

1. Under iMessage, unselect your phone number as a place to send and receive iMessages. You should only have your Apple ID/email address selected.

2. Turn off iMessage for 5 - 10 seconds. Just long enough for us to be sure it registered everywhere.

3. Turn iMessage back on. At this point you should only have your email address as the sender/recipient of iMessages.

4. Wait until you get the pop-up notification that “your APPLE ID is now being used for iMessage on a new Apple Watch”. If you forgot to turn off your phone number or if the notification says your PHONE NUMBER is being used for iMessage on your Apple Watch then go back to step 1.

5. After you get the notification that your Apple Watch is using your Apple ID for iMessage, you can change the iMessage settings to allow your phone number to send/receive iMessages. You can even make it the default. Just don’t unselect the email address and only leave the phone number.

I haven’t had the issue come back in a couple of weeks. Hope this helps.

Thanks u/Dee_Key

The messages are showing up on the other devices, not a problem. The problem is when I read them on my iPhone, they are still showing unread on other devices. If I read them on the other devices, they do get marked read on iPhone.