Just found a bug with ArcGIS Insights Online not loading on browsers with language settings that not set to English (US). My Chrome browser was using English (Australia) and ArcGIS Insights was unable to launch on ArcGIS Online.
However, it worked on a separate browser like Firefox. Upon closer inspection on Chrome's Dev tools, it seems this particular request was failing :
but the same request on Firefox works, the difference being the en-gb text.
My current workaround to this is to go to the language settings on your browser and change it to English (US).
Solved! Go to Solution.