HTML5 black screen if use blank template (but works with first and third person templates)

Hi, I am very new to UE4 and I am trying to build a UE4/HTML5 prototype for my research work.

I started with a blank template (tried with both mobile and desktop version) and got a black screen when build for HTML5 (in both Chrome and Firefox).
However, if started with the first person or third person templates, everything works fine in HTML5.

What are the minimum requirements / elements I need to add/modify to the blank template to get it work in HTML5?

I am developing on Windows 10, Visual Studio 2017 and Unreal 4.21.

Thank you.