Then I see no problem querying metrics at /prometheus/graph web interface. You may try to query for any metric.
If you can query Prometheus, there is no reason why it is not shown in Grafana.
Do you have all dashboards empty?
The last thing to check - please verify that the server time (underlying host where docker runs) and your local machine time (where you run web browser) is OK (what timezone is set - does not matter, the time should be simply correct on that timezone).