Answer by Michaeldx · Dec 09, 2016 at 11:23 PM
This one confused me too till I found the following on HPE's UFT Help Center:
"If you open a tab in an Edge browser with the Edge Agent for Functional Testing, you should perform at least one action in the browser to enable UFT to use the necessary mechanism to communicate with this tab."
Once I did that, it started working. Check this link for more info: http://uft-help.saas.hpe.com/en/12.54/UFT_Help/Content/Addins_Guide/EdgeLims.htm