Since a recent release of the Web App Builder for ArcGIS Online, there is a possibility to activate the Group Filter Widget by passing URL parameters to the app (as mentioned here: What’s new in Web AppBuilder (October 2019) ).
When I use the Group Filter Widget "manually" in Web App Builder in I can apply a filter and view the result. Then, when I close the widget or press "Reset" I get an unfiltered view of the layer.
However, when I use the URL-parameters to activate the widget I can no longer turn off the filter to get the unfiltered layer. When I press "Reset" or close the Widget the state returns to the one corresponding to the URL parameters.
I don't consider this to be the desired behavior. There must be a way to turn off the filter.