Changing to lodash's isEqual does fix this, however it also allows non-array arguments which is not the intention of the code. The underlying bug is that changeEntropyCdsSelection should be a no-op if the entropy data isn't present, i.e.

--- a/src/actions/entropy.js
+++ b/src/actions/entropy.js
@@ -55,6 +55,7 @@ export const updateEntropyVisibility = debounce((dispatch, getState) => {
 export const changeEntropyCdsSelection = (arg) => (dispatch, getState) => {
   const action = {type: types.CHANGE_ENTROPY_CDS_SELECTION}
   const entropy = getState().entropy;
+  if (!entropy.loaded) return;

This is a good example of where TypeScript would have helped ensure arguments passed to equalArrays were indeed arrays, which was the intention of the code. We don't want cases where we pass two non-array-but-equal arguments to isEqual.

While the intention of the code was to never call equalArrays with non-array arguments, we should also improve equalArrays to catch cases where we didn't do the right thing:

export const equalArrays = (a,b) => Array.isArray(a) && Array.isArray(b) && a.length===b.length && a.every((el, idx) => b[idx]===el);

I'll do a little more digging to see if there are other situations where we assume the presence of entropy data.

Hmm, this means it will return False if either arg is not an array and when the arrays are not equal which can make falsy checks problematic

Yes, that's fair, although isEqual will do the same. I think typescript is the way to go here, but that's well out of scope for this fix.