Google map in Gravity form is not showing or taking very long

I inserted a Google map in a Gravity forms form with a HTML field. The field is conditional, untill you choose a course it is not visible.
It does work but not always and when it works it takes very long before the map is visible.
The url of the page is http://bhvflex.nl/bhvflex/inschrijven/
Thanks in advance, Ariane