Well, the error message is telling you the problem... Somehow, you have the questionnaire installed without the version file being present. Look at your "mod/questionnaire" directory and see what's there.
The error message appeared only on iPhones, using the moodle app.
I copied everything (again, but from today) from github into mod/questionnaire and called the admin page from the browser to get it installed. Now it works.
Nobody will ever find the reason of the missing file version.php