Half the tabs opened in IE mode hang and display error

Hello,

I am a developer at MicroFocus working on a functional testing product, and we are trying to integrate IE mode support in our product. We are using these command line flags to start Edge in IE mode: "msedge --ie-mode-force --internet-explorer-integration=iemode".

In our testing, we found that when opening a new tab in this IE mode, half the new tabs opened will display a 404 "The webpage cannot be found" message. Attempting to navigate in any of these tabs will just hang indefinitely (the UI is not hanging, but the tab is showing the loading icon).

When we try to start Edge in IE mode with our product running (which hooks a dll into every running process, and detects running windows and some other things), it seems that the hanging behavior is always happening in all the tabs.

Attempting to attach to the IE process on startup (we do this by setting SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\<program_exe>\Debugger=vsjitdebugger.exe) seems to make things worse, the IE process doesn't even show the "404" message and hangs before starting the second iexplore.exe process.

To me, this sounds like a timing issue or some race condition which is made worse by anything that slows down the execution (like a debugger, or programs that hook DLLs).

Is there any way of solving this issue? We can provide memory dumps if necessary.

Thank you.