I recommend you reach out to Esri Support to open a support ticket. Esri Technical Support is already aware of this issue and should be able to provide guidance. They’re tracking it as BUG-000156053
In a nutshell, the Layer IDs stored in the Dashboard JSON are out of sync with those stored in a map/feature service. This can happen (for example) when a dashboard element gets created by pointing to a standalone layer, and then at some point afterward, the service that backs the layer gets re-published/overwritten and the layer IDs do not get preserved.
One possible "fix", is to use the ArcGIS Online Assistant first to figure out the ID of the feature services being used by each widget and second change the LayerID for each widget in the dashboard.
Martin Copping
Product Manager, ArcGIS Online - Dashboards