Keyboard Functionality Not Working When Publishing as HTML5 only

I am using Captivate 2017 with a default playbar configured in the Skin Editor.  We are trying to make our courseware 508 compliant but I'm running into an issue:

While I can tab through a project that has been published to HTML5 or previewed as HTML5, pressing Enter when on a playbar control (rewind, forward, back, mute, any playbar control) does nothing.  The Enter key function is not an issue on a Click Box if a keyboard shortcut is defined; this is only an issue with the playbar.  To add to the mystery, Enter does appear to be work if published as SWF but we have a mandate not to use SWF.

Can anyone help with this incredibly frustrating issue?

Thanks! ~christel