As a non English speaker (native) I struggled with the puzzle where I have to fill in words. I filled in cape, but the answer was vest. I should have derived the answer from the sentence given and the solution was like 2 last chars + 2 first chars of the words in sentence words. That's not logic, that's pattern matching. Found it disruptive to suddenly needing to enter something. I am among 30 percent of that run.

Implement a questionnaire whether one is native or non native. I observed it a lot of times: as non native speaker, such things are solved easily when there is a choseable answer given. But even with obvious answers and type-to-fill-in, I saw lot of struggle .

May be it's a topic for the IQ testing or some PhD you can deliver data for :)