Models broken when updating from v4 to v5/v6

I’m not sure what the problem is with Amazon Sumerian models. But I noticed something.

If I take the above broken Babylon example, https://playground.babylonjs.com/#6I67BL#321, and downgrade it to 4.x, it starts to shake like this:

I am also experiencing vibration like that when upgrading from 4.x to 5.x:

Note the face shape is all distorted too.

Does this provide any clues?

Here’s the open source: amazon-sumerian-hosts/packages/amazon-sumerian-hosts-babylon/src/Babylon.js/HostObject.js at mainline2.0 · aws-samples/amazon-sumerian-hosts · GitHub

(search for “animation” and you’ll find lots of results).

Do you see anything wrong there?

I looked at https://doc.babylonjs.com/whats-new, but I don’t see anything obvious.