Dude, where are my wolfs?

Background first. I am currently in the middle of my first castle build and it seems I might have a bit overshoot with the size (survival solo build, no mods or commands). So I thought: "Well, I need MORE stone" so decided to build stone factory.

The idea was simple and not very original – found Graydwarf Nest, surrounded it with natural wall, got a sizable pack of 2-star wolfes to run around. I've also added a small flat surface for the chest shed at the height of the walls. I have tested the walls to be completely safe and non-climbable. The nest was just at the bank, so instead of digging a hole I've simply raised the ground to cover it and protect form the wolfs.

There was also a small island pretty far in the sea – perfect place for a recovery farm. I have set up a small base there and built a bridge with gates on both sides to easily transfer the wolves to the nest. The bridge ended at my raised flat surface, so there was no access to it without jumping. The Island itself was far enough for the wolves not being triggered by enemies on the opposite bank and the water was too deep for trolls (quite funny when they just stand in the water waiting for my arrows). The only spawn on the island were occasional deers, which is perfect for wolf farming.

After setting up everything, I had 4 2-star wolves killing graydwarfs in the enclosement (and one puppy) with about 100 meat and 8 safety wolves + 2 puppies on the island. This was running smoothly for about 2 hours (even had sulfur event in the meantime with no turbulence for the operation) – so I left it running over night, happy to harvest in the (RL) morning. I've built myself a little pillar (probably too low…) in a proximity of the nest and went to sleep.

That game really makes you humble, doesn't it?

On the next day, I am armorless in front of my half-destroyed island base in the infinite respawn loop with a single skeleton standing on my bed. There's not a single wolf on the island, but also no wolf drops – no pelts, no meat nothing.

The bridge is intact, both gates closed and untouched. Wolves in the nest – dead (sort of expected with that amount of meat). Apart from their drop, just a little bit of wood and stone and other graydwarf drops. All wolfs have died in the same corner – far from the nest. My chest shack wall is destroyed together with 2 chests.

So big question: what in earth could've happen? I expect I dah initially died from a night-dwelling troll who also destroyed my shack's wall. That would be ok. But where are my island wolves? And how did that skeleton got onto the island? My best guess so far is the "Skeleton surprise" event – skeletons swimming to the island they could pull the wolves away – but I'd expect quite a lot of skeleton bones lying around and there was none. And I'd expect more skeletons as well… Is there any way to find my wolves? It took me ages to catch one of them…