Description
All locations of the space-time cube have time series with constant values (not necessarily the same constant value at each location).
For the Forest-based Forecast tool, if the Entire cube option is specified for the Model Scale parameter, variation is required at some locations to fit a forest-based model. In this case, all forecasts will be equal to the constant value at the location.
Solution
Use a space-time cube and analysis variable that have variation in some locations.