Quiz somethimes getting stuck; no Results slide; Cp not responding message

I am using Captive 9 on a Windows 10 machine with 16GB RAM. The Captivate project I am working on contains 55 slides of which 8 slides are "knowledge" questions (not scored) and 10 slides are multiple-choice slides (scored) selected randomly from a quiz pool. For some reason, when previewing the project, the quiz often, but not always(!), gets stuck at slide 4 or 5 and will not move beyond that point. The quiz is controlled with a "Submit All" button. There is a "back" key but no "skip," "clear," or submit keys. The times that the quiz successfully runs through all 10 questions, the results page does not display.

It's a real puzzle as it had been working fine until a couple of days ago. The one thing that was changed was that a certificate (and text input to capture the learner's name) was added, basically to try it out, and then removed. The quiz slides have been edited quite a few times to adjust for placement, etc. Is it possible that something was deleted that should not have been from a quiz slide? Is there any way that I could check for this?

The pause does not appear to be tied to any one specific quiz slide and, as mentioned earlier, can pause at slide 4, slide 5, or slide 10.

Another, possibly related, problem I am experiencing is that I get a Captivate Not Responding message often! It typically resolves itself but can take a few minutes to do so.

Any suggestions?