I'm using Start11 V2 but this also was happening to me in V1. I finally decided to report it after upgrading to V2 and having it still happen.

I group all if my icons in my taskbar together. So I have multiple Edge windows open, but only one Edge icon. In order to determine which Edge instance to use, I hover over the icon and little preview windows pop up above the taskbar of each Edge instance and show me, and then I can pick the one I want. I also do this with all my other apps.

I've noticed with Start11, if I have a second monitor connected to my laptop and then unplug the cord to go back to just my built in display, the taskbar no longer shows me preview windows of my applications. The only solution I've found is to restart windows explorer.

I'm hoping you can find a bug fix for it so I don't have to keep doing this! If you need any further information let me know.

Thanks!