Hi Paul, I've tested your override. It now correctly generates JSON-LD for breadcrumbs, but it has several errors in the microdata that weren't there before. It's missing the position and name fields for the "you are here" or "icon" element because it now has an itemListElement. Also, the element that currently has position 1 (should be 2 if "you are here" has position), which is Home, doesn't have a name field.
The previous override, located inplugins/system/helixultimate/overrides/mod_breadcrumbs, correctly generates microdata in HTML; it's just missing the JSON-LD. The idea would be to improve that by adding the JSON-LD or improve the current override so that it correctly generates the HTML with microdata because Google reads both. When it's ready and tested, add that to the plugin, not the template. When you have another version, you can share it or send it to me so I can test it.
Regards