Hi,
When me and my team try to add resource header customization template, it breaks the page without errors on console.
We follow the provide Overview guide step by step, the only difference we found on your online example, is that inspecting javascript on yours example you use SystemJS and our use Webpack (vue-cli project).
We try to search similar issue by without success.
I can attach a small example, just run npm install and then npm run serve
Attachment:
helloworld_dd779c0.zip