Reported and initially investigated by RMED, Juan Castillo. Juan proposed a temporary fix that allows to run the model but may Mike pointed out that it may not be the best approach as it risks violating flux conservation.
Issues that arise from the coupled mode should be communicated to NEMO WG Air-Sea interaction: https://forge.nemo-ocean.eu/nemo/nemo/-/wikis/wg-airsea (Guillaume Samson).
Incidentally, CMCC will attempt WWIII coupling to NEMOv5 in their MedSea configuration.