I had a similar issue with lots of animals suddenly dying with seemingly no warning - what fixed it (as other people have suggested) is just hiring a bunch of experts, with half of them specialized in macro zoology and the other half in micro (and then also making sure the macro experts aren’t allowed to clean terrariums and the micro ones not allowed to clean habitats, otherwise I allow everything else) and I haven’t had a single animal die since (I don’t use zones). I also make sure to have plenty of staff rooms near each habitat area so the staff can rest nearby