This still persists for me on 2020.48.26 and has continued across a full factory reset of my Pixel 4xl. I will go out on a limb and assert that it isn't caused by RCS or MMS messages. But it occurred to me that I have used the SMS Backup and Restore app to transfer and restore text messages across a sequence of Android phones and across my last factory reset. I am wondering if any of you who have suffered from this issue have used the same or a similar app for restoring text messages, including MMS which the default Google cloud backup doesn't. My theory being that maybe it restores the message database into a state that is confusing the process of transferring new messages to the car.