Message app automatically marking messages as "Read"

So for a while I thought that I wasn't getting notifications for texts that I was receiving. After some troubleshooting I think I've nailed down what is actually happening. I turned on "Read Receipts" and did some testing. I'll send a text to a person, exit the messages app, and lock the phone (this last part is optional as I can go into another app and get the same result). No response, no notification, no idea if I've had a reply to the message I sent. I'll check back a few minutes later and find that my recipient had IMMEDIATELY messaged me back. I was not informed. However, the recipient was told that immediately after THEY messaged me, they received the "message read" indication. This tells me that our phones are marking the first message they sent as read, even though I didn't even have my messages app open.

So it's not an issue of iOS 14 not notifying users that they have a new message, it's that they are being marked as read automatically.