@Harvy66:
When I upgraded from 2.2 to 2.3, the RRD stuff broke for me and I had to reset all of my, now called, monitoring data. Then it suddenly worked again. If you need your historical data, export your data, then trying to reset the data to see if that "solves" it.
I didn't realize there was an option to reset the data under the "Display Advanced" in the monitoring. That fixed it. Thanks!