Retroactive “Message Failed to Send” notifications

Over the past 2 days I have been receiving “Message failed to send” notifications for messages that are hundreds to thousands of days old. I know for a fact that this is incorrect, because when I tracked down each message, nearly all had a reply in direct response to the message I (successfully) sent.

I ended up going through the entire conversation history of the text threads for these people and deleting all the ones with red exclamation marks, but new ones pop up every time I reboot my phone. What gives? I have posted other topics regarding iMessage & not being able to deregister. Now it seems to be turning into a myriad of problems. Did the last update screw up Messages/iMessage? My network carrier says it has nothing to do with them. I’ve even gone as far as restoring the phone entirely.