The table (mysql) timezone is system. System is Europe/Berlin. Grafana is also running on the same system. The grafana Timezone is also Europe/Berlin (CEST)
Have you found the reason of the issue OR is it still happening?
If this is still happening, then can you please try to reproduce this on the latest stable version of Grafana with your data as your data seems to be a bit unique and could help us to understand this phenomenon on the latest version.