I'm not sure if this is a bug or intended behavior, but if you run the "Rebuild Address Locator" tool on a locator that is in your current instance of ArcGIS Pro, when the tool completes, the locator is completely removed from the current project and has to be re-added. If you run the tool by scheduling the GP tool, this does not happen. But if you have ArcGIS Pro open and rebuild the locator, it will be removed. Very annoying to have to constantly re-add the locator.