Hi PeterMMC, sorry for the inconvenience!
Mantine moves you back to the Pokemon Center when the quest fails to return your Pokemons to your party. However, this isn't your issue. The problem you have is that the quest failed to return your inventory, and therefore you are missing a lot of items, including HM03 - Surf. Fortunately, your inventory is still saved, so I'll be able to restore it today.
Until then, please do not try reentering the quest. This could overwrite your saved inventory, and restoring your inventory will require a lot more time.
I will let you know once a fix has been made.
Shizeria