Error using Material Theme in GitLab Pages

[carsten-bo]

When opening a notebook using the material theme, the search plugin and theme switch button is not being shown. The browser shows follwing error:

Uncaught TypeError: X is not a function
    at Subscriber.ts:21
    at Subscriber.ts:137
    at bundle.ts:254

I use gitlab pages for serving. When serving locally with mkdocs serve command, everything works well.
Not sure what the exact issue is and if it's caused by mknotebooks plugin.