Appointments+ not working in BigBang theme

Hi

We have a problem using Appointments+ We cannot choose the day or time slot when using it within a client's website. When switching themes to twentyfifteen it works fine switching plugins won't change anything. It is safe to say it has "something" todo with the theme. Though, there are no js conflicts / errors. Hopefully someone has an idea on how we can pinpoint/fix te problem.

The page is on: http://www.winkelgebiedbosenlommer.nl/afspraken/