const camelcaseKeys = require('camelcase-keys');

At top level, array members are turned into array elements.

(a = [{test_one: 1}]).test_two = {}; a;
// [ { test_one: 1 }, test_two: {} ]
camelcaseKeys(a);
// [ { testOne: 1 }, {} ]

At lower levels, array members are lost.

(o = {deep: [{test_one: 1}]}).deep.test_two = 1; o;
// { deep: [ { test_one: 1 }, test_two: 1 ] }
camelcaseKeys(o, {deep: true});
// { deep: [ { testOne: 1 } ] } }

I realize this is bad practice.
However, that this library mangles them and, in particular, inconsistently is I think problematic.

Proposed solution

map-obj already has the ability to handle Arrays.
Simply remove the extra function at module.exports and export camelCaseConvert directly.

Side note

Doesn't map-obj already have a caching mechanism?
It seems a little redundant to me to have a caching layer in this package.
Maybe I'm missing something?