There is nothing mad about the dashboard's behaviour - it either gets the data it expects or it does not. :)
Some basic troubleshooting for Prometheus/Grafana:
* curl the prometheus endpoint to see if you get the expected metrics (curl ...:15692/metrics/...)
* check Prometheus target scraping information to see if the above endpoint is scraped successfully
* optionally, check in Prometheus UI, that you can query/visualize the data
* check if you can add a simple panel to Grafana (add new and put a metric name as the query)
If nothing works - I'd start from the top. If it used to work, I'd start from the bottom of this list.
Best,