Is it with the same type of laptop and cable? Curious since @AvikChatterjee-8589 is able to reproduce.
Would like to clarify as much as possible since those feedback forms tend to be a black hole where I expect to hear nothing back. If that's all you can offer I will probably just switch to Brave or Chrome :/
Okay, I took some time to find steps to reproduce, that still work on latest edge (88.0.705.50)
Plug in an external monitor (I have an MSI Optix MAG272QP) via USB-C
Open a new window, go to for example peanuts.com (then open some more tabs in the same window, I will explain why)
Make that window fullscreen on the laptop's own monitor
Switch to a different space than the fullscreen peanuts.com window
Click Apple menu -> Sleep
Wake the computer
The peanuts.com window is now gone, typing peanuts.com in the url bar will let you "Switch to this tab", and if you had more than one tab open in that window, it will now reappear.
If you only opened one tab, like I did while testing this, you're now stuck with a permanent missing window that contains only the tab peanuts.com, but edge won't let you switch to it, instead, clicking "Switch to this tab" just opens peanuts.com in a new tab.
@YuZhou-MSFT any update? Did you see the reproduction steps?