Silkie - Sudden death???

[Wyorp Rock]

1 1/2 hours ago I was preparing stuff to clean out the Silkies' temporary cage but when I walked up to it, I saw that our Lavender was dead. She was fine an hour before so I'm not sure what caused her death. I'm really heartbroken as this is our 5th Silkie to die(Other 4 died a few months ago).

The other 3 are doing fine and are actually very confused and freaked out. I put them in a large plastic tub so that I could clean out their cage.
I put them back in the cage and they're currently sleeping as it's a half hour before 3am.
I gave the other 3 some Corid directly just in case. They were actually getting corid in their water since Saturday. I at first thought parasites but I checked all Silkies and they're are clear of them, even their poo is clear of them.

All Silkies are around 4 months old.

What would cause a pullet to suddenly die?
What should I check for?

I know that. I already used safeguard the day I got them.

I'm sorry for your loss

Since this is the 5th one that you have lost in the last few months, it's time to get a necropsy so you can figure out what is going on. Refrigerate the body and send it to your state lab. https://agri.ohio.gov/wps/portal/gov/oda/programs/animal-disease-diagnostic-lab/welcome

In the meantime, if you can provide photos of the remaining Silkies, where you are keeping them (housing), their poop and tell us what you feed, including treats, we may be able to give you some suggestions.

 

[KikiDeAnime]

In the meantime, if you can provide photos of the remaining Silkies, where you are keeping them (housing), their poop and tell us what you feed, including treats, we may be able to give you some suggestions.

The other 3 will actually be going to live outside either later today or tomorrow but they currently live in a large cage(Ones that they sell for rabbits but bigger). They are currently in quarantine until I had deterrimined that they were good enough to go outside to live near our other hens.
I'll get photos of them later, I'm going to be giving them a bath soon as their feathers are very dirty due to one of them deciding to knock the water dish over and getting food all over themselves.
I feed them the Bar Ale brand for feed and meal worms as treats.

 

[Wyorp Rock]

The other 3 will actually be going to live outside either later today or tomorrow but they currently live in a large cage(Ones that they sell for rabbits but bigger). They are currently in quarantine until I had deterrimined that they were good enough to go outside to live near our other hens.
I'll get photos of them later, I'm going to be giving them a bath soon as their feathers are very dirty due to one of them deciding to knock the water dish over and getting food all over themselves.
I feed them the Bar Ale brand for feed and meal worms as treats.

Is that chick starter or layer feed?
Poop photos are always welcome too.

Personally, if you don't know what caused this sudden death and you had another die of some illness some time back, I would keep them all quarantined for a while longer until you figure this out.
It could be genetics, Coccidiosis or something that is fairly innocuous, but then again, I would worry it could be something that can be spread to other birds.

 

[KikiDeAnime]

Is that chick starter or layer feed?

It just says Poultry Feed on the bag.

 

[Ladybird CA]

silkies are also prone to brain injuries from their vaulted skulls. I had a rooster that died because a smaller rooster pecked it on the head.

 

[Wyorp Rock]

It just says Poultry Feed on the bag.

It would be good if you looked at the ingredients/label of your feed. See if it's layer or starter/grower and what percentage protein is in the feed.