I recently had my iPhone 6s replaced (strictly speaking, a battery repair). Since I restored my backup to it (iOS 12.2), every time the phone reboots I get an alert about a message that failed to send from, at the time of writing, 2505 days ago. This dates it to 3rd June 2012.
The old phone did not complain about this unsent message, so I suspect that something may have been inconsistent in the restore. I don't get the error either on my iPad or MBA on the same account / phone no.
Short of trawling through every message history with every contact around that date, I seem to find no way of searching on-phone for messages from that date. I have also found this older post How can I locate an iMessage from 1-2 months ago? Possible? which referenced how to access the iChat transcripts on my MBA at
~/Library/Containers/com.apple.iChat/Data/Library/Messages/Archive/ but I'm limited in how I can search with the Finder. I can't seem to even get root access to the directory in the terminal.
I've deleted some older conversations from 2012 which I no longer need, but a reboot still brings up the alert, so I suspect the message in question may be in the history of my current contacts.
How can I reliably track down any messages for a specific date?