In case it's of use to anyone else, this "stuck" charging data has persisted across TCU swap/program, 12V disconnect, Sync Master Reset, Sync SW update (3.0 to 3.4), full HV battery discharge (0% + 1kWh reserve and the full SNS warning), L1/L2 charging sessions and configuration/toggle of value charge.
If anyone has any info on other things to try or look for, I'm totally down. I have a pretty extensive toolset for capturing CANBus data now - bought a second CANDue to have full capture on two busses (so it can MITM comms if needed). Pretty sure this data is stored in the APIM but I'd love to be proved wrong on that. This may literally be the last charging session I had before the MFM app was shut down - I just can't imagine how that data would be dependent on MFM to update. Though I suppose stupider things have happened.
Also going to reach out to my Ford support contact and see if they need beta testers or feedback.