I put the setting back to "Block (Default)". It continues to work. Maybe the toggling of that setting cleared whatever went wrong.

I have got it working.
I changed the 'site setting' : 'Insecure content' to "allow" (it was 'Block (default)')

Hi Kiriak, It works in the incognito mode as you suggested. Any idea how I might get it working again in normal mode?

The hover pop-ups are not appearing for me anymore when using google Chrome. I updated Chrome to "Version 81.0.4044.92 (Official Build) (64-bit)". I have disabled ad-blocking for the site.
The hover popups work using Firefox 74.0 (64-bit). Is there a setting I need to change?