Unexpected Output from Enum module function

I was reading through the Enum module functions and copying them into the repl to get a feel for how they work. I pasted the following into the repl from the documentation.

Enum.chunk_by([1, 2, 2, 3, 4, 4, 6, 7, 7], &(rem(&1, 2) == 1))

Instead of it returning this, as it should per the docs: [[1], [2, 2], [3], [4, 4, 6], [7, 7]]

It returned this: [[1], [2, 2], [3], [4, 4, 6], '\a\a']

What’s going on?

I even got the same result when I used an online repl.
https://replit.com/@threetriangles/MinorWaryGraphicslibrary#main.exs