I have just installed the gantry5 plugin as well the hydrogen them and the helium theme. if i activate the helium theme and restart my site then i always get this error
Server Error
Sorry, something went terribly wrong!
400 - Template “blog.html.twig” is not defined.
For further details please review your logs/ folder, or enable displaying of errors in your system configuration.
Whatever page you are loading is defined to use a page template not defined in Helium theme. Change the page template to something that is available when you have the Helium theme activated. Alternatively if that page template is needed you could inherit the template and make changes on the inherited template to ensure you changes stick when theme is updated in the future.
I tired inheriting the Helium template and so far it did not work as expected. Wish there was more documentation on this theme or even a skeleton, but it is early so we may see something soon. There is a lot of documentation on Grant5. I just need to find out how to assign modular templates to a page once Helium theme is activated. Seem I can activate another theme where the modular page template is available and the switch back to Helium.