After I installed the latest Visual Studio plug-in, the interrogation function was not able to detect any HTML controls inside Internet Explorer from a Web Adapter. I tested with Pega Robotic Automation 8.0.2014, 8.0.2019(SP1) and v19.1. I received same result. However, if I re-install v8.0.1067 plug-in, then interrogation works.
The investigation of the related Support Case concluded that there was an environmental setting on the user's machine that did not allow IE to start as a 32bit process which is necessary for Robotic Studio and Runtime for control creation.