Issues with starting a poll during a webiar

Dear community,

whenever I try to open a poll during a webinar the original presentation (in my case Keynote) is closing down - doe anyone have an idea why this keeps happening?

I generally share my screen with the advanced and portion of screen option. Keynote is opened in rehearse slideshow mode. I then click on polls and when I try to launch it keynote is closing down completely. 

I have therefore given up on using polls, which is not really the perfect solution.

Thanks so much for your help!