Hi Somedia,
I think the issue is related to template you use (gridbox). I'm trying to make a temporary menu item using default template protostar here
zahnarzt-al-dulaimi.de/agent-test and it looks like the module is working good there.
I'm not familiar with gridbox template but it looks like gridbox compile all js into one file (to decrease http request I think) but the problem is the js file not compiled correctly / the order is incorrect.
As I said before, can you try to install
extensions.joomla.org/extension/jquery-easy/ on your website and see if it will solve the problem or not.