This broke unexpectedly in July. Hot fix came about a month later. Upgrading to v4 completely broke backwards compatibility.

Wasn't expecting that from an aws created lambda solution

This is what I use in production right now. It works well once you figure it out, but backwards compatibility with the previous Thumbor based version isn't as good (or at least correctly documented) as they say. And the previous Thumbor based processor just stopped working one day. It's not as robust as a system as I expected.

That's unfortunate, I've only just begun rolling into a new project, so I can't comment on how it used to be.