Quiz Questions not Displaying in Safari Browser

Captivate 2019 publishing to an in-house server as HTML5.  Volume is about 200 completions per day.

After a review slide, quiz questions stall out for a small set of users accessing via Safari.
No advanced actions on entry to quiz slide, quiz slides tend to be stock questions (no audio, video, etc.) and no timings or actions other than submit.  Questions are drawn from a question pool of approximately 2x the questions used.

The background displays, but not text captions. Neither stem nor distractors show up. For multiple-choice, the radio buttons for selection are visible but not selectable, nor is the submit button.

Quiz content displays properly on Edge, Firefox, Chrome, etc. and windows-based machines.

Anyone have any thoughts?