I had the same issue. There seems to be an issue with adding the layers via Project Overview page when you Click on the "Dispatcher Map" or "Worker Map" to start adding layers. I found that Workforce creates a series of features and services at the time of Workforce project creation under your organizational content page. The work around for now is to do the following: Login to your organizational account Navigate to "My Content" tab. Notice the list of folders along the left side of the "My Content" list. Select the folder that is named the same as your "Workforce Project Name" Under that folder your list will update to show the assignments layer, dispatcher layer, workers, and two web maps (dispatcher and workers). Select either map you are working on to add layers traditionally with any AGOL web map. Add your layers and configure as needed then "Save" the map. Once that is done open the desired Workforce map (i.e. dispatcher) to view. I hope this helps for now until ESRI corrects this issue with the Workforce!
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