Make sure the router had correct time before and also after the switch down period. Wait for the graph saving period and recheck the graphs. After reset the data is lost.
Maybe look at mikrotik dude...
The router syncs its clock from NTP, and the sync seems to be working. The graph saving period is 5 minutes, and the problem hasn't solved itself in a day. The graph data is saved to internal Flash, and that's how it survives over restart. Just in case it's not clear, I didn't expect the data to survive the reset. I don't really understand how the Dude would help in this case, could you explain in a bit more detail?