They've missed one of the module updates then that enables this feature I would guess.
We understand there are several (maybe 15 or so) different modules (ecus) that can be updated, each has to be selected (and then configured correctly) by the engineer.
If you def have the latest BMS update, then that would suggest, that the AC charge unlocked functionality is part of a different module/ecu update that hasn't been applied to your car. Or I guess it could be the configuration part that's not been done correctly on the BMS module/ecu.
This is exactly what is REALLY annoying so many of us.
If the car goes in for updates, they should make 100% sure that EVERY item has been updated correctly to the latest version.
The system they use, does not do this and it must not have the functionality to check afterwards that it has ALL been updated correctly.
This is leaving everyones cars slightly different, which is an absolute support nightmare.