The problem appears to be browser related. Testing Vega-Lite in my production base, settings do not load in the Safari browser, but the settings load when using the Chrome browser.
Testing Vega-Lite in a new base which only has one table with 4 colmns and ~1000 records.
My base is also large and complex and I was also using Safari - but switching to Chrome does it for me too! Thanks for letting me know, really appreciate it.