Course stuck at quiz question

I have a couple users who are experiencing issues on quiz question slides in my Adobe Captivate (2017 Release 10.0.0.192) course.  This has not been a widespread problem.  Currently there are 3,600 successful completions and I've only been made aware of this problem happening to two different people.

Here's what's happening:  The user can get through the main portion of the content with no problems.  As they arrive on the first question slide they can read the question, select their answer and press the submit button.  The immediate feedback does not show up and the slide does not progress to the next question as they continue to click on the slide or press 'y' to continue. Essentially they are stuck at that point and cannot progress.

I have removed their enrollment and had them start over again.  They have restarted their computers.

Playbar on question slides is disabled to prevent skipping. The course has been published as TinCan and is working fine for thousands of other people as I mentioned above. These users are using the same hardware/software that most of the other company is running.  Windows 8, Internet Explorer 11

Any suggestions/ideas would be greatly appreciated.  I have to assume this may have something to do with their workstation configuration and not the content since so many other people have been able to successfully complete the course but I just can't figure out what would cause this type of behavior.