When the Evaluate Optimal Number of Groups parameter is checked, the tool will solve for 2, 3, 4, or up to 15 groups. This process can take a while to complete, especially when the Spatial Constraints parameter is set to No spatial constraint and the number of features is large.
Uncheck the Evaluate Optimal Number of Groups parameter and use a different strategy for deciding how many groups to create. Once you identify the optimal number of groups for a fixed set of features, the Analysis Fields value, and the Spatial Constraints value, you do not need to repeat this evaluation step. If you change the Analysis Fields, Spatial Constraints, or Input Features values, however, the optimal number of groups (as determined by the pseudo F-Statistic) may also change. The spatial method options for the Spatial Constraints parameter solve faster than the No spatial constraint option.