Could you post the persistence strategy used for these Items? If you are using every change and/or also persisting other than 15 minutes, then you will get some funky values, which is what I just got when testing this out.
BTW, if you do not have a way to see the data, you might want to look at…
This will give you the average 3h forecast for the day. I think you are looking for the SUM of the 3h forecasts for the day.
