This tool first assesses if there are any isolated clusters of features based on the Spatial Constraints specified. Grouping begins with disconnected clusters already forming groups.
The Spatial Constraints parameters determine which features can be grouped together. If you are seeing a message about clusters of disconnected groups, you may want to modify your Spatial Constraints parameters. More information about how the Grouping Analysis tool works with disconnected clusters of features is described in the tool help. Selecting the K Nearest Neighbor Spatial Constraints and increasing the Number of Neighbors parameter until there are no disconnected groups will ensure that both spatial and data relationships are incorporated into the grouping algorithm.