Captioning Box Problems

Earlier today, when  I was captioning a meeting, the presenter played a video.  Upon playing the video, the video took over my entire screen.  I had difficulties exiting the full-screen mode of the video, and once I was able to, the captioning box that I caption into was no longer there.  The meeting had to be interrupted, and the host had to once again designate me as the captioner.

How can this problem be fixed? 

Thank you for any suggestions!