Leviathan

So, had a weird experience tonight with one of the island creatures. A leviathan? Can't remember if that's the name. Either way, I was doing a jaunt around the shore of my island to see my biome choices and saw a leviathan like.. right off my actual island. With full stamina I could easily just swim from shore to the old boy. So, of course I did.

Once I got there, I like… Slid around on it. As if it was tilted or very steep or covered in grease. I can't really explain it better than that. Definitely glitchy.

So, I harvested 28 before it began to sink. I booked it back to land (nearly drowning) and thought.. that was weird. Anyways, I got back to land and turned around to look back wistfully.. and the leviathan was there again! Before anyone says anything I'm certain it sank (or was sinking) before it reappeared.

Anyone had an experience like this? Should I report it?

Edit: I had enough on hand to slap together a raft, as night had fallen and figured for more chitin. About halfway out to the leviathan, it just blinked out of existence. Never to return.