During the Quest “To Shell with it”, it is easily possible to clear the entire zone without getting all of the Giant Crab Meat in Coral Pools. An increased drop rate of this would be wonderful as reloading the zone just to complete a side quests feels awkward.
Its a bug but it does not prevent you from completing the quest, like you I cleared the area thinking this is weird but as soon as I left the area the quest updated to say it can be handed in.
Leaving the area and then re-entering will update your crab meat count. For me, I walked out and back in (after killing lots of crabs, apparently without getting enough meat) and the objective instantly completed.
I think the meat is still dropping, the quest objective just doesn’t update properly until you force a reload.