Different log in location, peaceful mobs despawn, ice on Lake

I just started a relatively new singleplayer world, found a village close to spawn. Built a cobblestone wall around it. ( This was over multiple log ins and outs) I logged out. Next time I log in, I'm at the same x and z coordinates, but my y level is way deeper. I'm inside a cave, y level probably negative, I can see dripstone and multiple monsters. I copied the world and switched to creative. I headed up, and saw that a nearby lake had ice on the edges. There's were multiple water bodies as close as the lake, but only it had ice. It was night time. I went around to see what else had happened, and saw that all animals in pens that spawned with the village (1 horse and 2 cows) were dead, they had dropped meat and leather, and so had my iron golem. All my villagers were gone too. I could still peaceful mobs outside the village, and no drops outside. All happened on same world at the same time, so I made only one report. Also this was a oak village, had a gravel mountain nearby, in the plains biome, so ice was not possible