Layer is for laying ducks, but All Flock Crumble doesn’t have the extra nutrients for making eggs. All the extra stuff could be bad for ducks that aren’t laying (out of season or males).
Maybe from here on I would recommend you keeping the food and water outside the coop to lessen the chance of mold and encourage you keep the water refilled at all times and then see how they do?
Here’s a link on poultry dehydration. It mainly discusses chickens but I assume it’s the same for ducks:
https://www.backyardchickens.com/threads/dehydration-symptoms-cure-and-prevention.678722/
Did/does your birds show any of the symptoms in this thread? And maybe provide a pictures of your...
Perhaps they are dumping it out or bathing in it? My two ducks still have plenty of water leftover in their tub at the end of the day, it shouldn’t get dry.