Hi Tejas,
Thanks for your response, see my answer to Masa above, I found a solution.
I had already upgraded the UI5 runtime to 1.22.8 and that did not fix it.
It appeared to be trying to load gold reflection theme, so by passing the theme in the URL as a parameter like &sap-theme=sap_bluecrystal - the isue seems to be fixed.
Cheers,
Brad