I'm testing the new filter widget available in Web AppBuilder that came with Portal for ArcGIS 10.5. When I create a filter with preset values entered, everything works fine. However, when I check the box to "Ask for values," the filter won't load.

In the filter tab, I can see the filter name with a load icon next to it. However, it won't finish loading and I can't open/use the filter.

I've looked through the help documents about the filter but can't figure out what the issue is. Any help would be appreciated.
Thank you,
Lucas