The participating locator in the composite locator cannot be loaded; it may be invalid or missing.
Solution
Open the Locator Properties dialog of the composite locator to reload or remove the participating locator in question.
More information
A participating locator may be missing because of an incorrect path, network, server, or portal connections. You can check the location of the participating locator or whether the network connection is correct. If the participating locator is stored on a server, confirm that the service is up and running.
A participating locator may be invalid because it is not a supported version, it requires a license, or the role of the locator is not supported. Locators created prior to version 10.0 with the Create Address Locator tool are not supported in ArcGIS Pro. Check the supported version of the primary locator role of the participating locator.