You experience issue when trying to log on to Grafana. You are sure that user name and password are correct, but Grafana will not let you in. This issue might arrise because locks are currently blocking the database.
Even though there might be other ways of fixing this, one solution I found to be successful was to clone the Grafana database and then copy this database back. This has the effect that the locks blocking access to the database is released and you are able to log back into Grafana.