Grafana is empty after install+changing admin password

Hi there, I made some progress to install Grafana on my webserver with https and as reverse proxy; so I installed the grafana package, made adjustments in apache’s virtual hosts 443 file:

ProxyPass "/grafana" "http://localhost:3000"
ProxyPassReverse "/grafana" "http://localhost:3000"

and in the grafana.ini:

   domain =
   root_url = %(protocol)s://%(domain)s:%(http_port)s/grafana
   serve_from_sub_path = true

and then re-started grafana service and apache.

For the first start, I entered then

I get the screen to login and to change the admin password, but then I see a black dashboard with only some elements - not all the greetings at first start. I can’t edit a dashboard (error: TypeError: i is undefined) and when I click on the grafana symbol, it enters the URL without the “/grafana” at the end.

Please help me to fix it and get a nice and pretty Grafana!

Just to add a detail, maybe important:

When I start the same grafana instance directly on the server (http://localhost:3000) - everything works fine.