Hi Sravan,
Blue Prism modern browser mode does not quite work in the same way as IE mode, i.e., Application Modeller has access to all open tabs/instances. When looking up elements, Application Modell goes through all open pages to find the element. Tracking ID which was introduced in v6.9 allows you to limit the search to a specific tab/page in case you have more than one element meeting the same element definition.
That being said, I would suggest you create a support ticket to have your case investigated around iframe if you have not had success in spying elements within it.