System.InvalidOperationException (SessionNotCreated) and Browser Window opens non-automated on some machines

[andreas-neubacher]

When I drive Edge with Selenium (.NET) on a dev machine (Windows 11), everything works fine.

When I do the same on an office PC (also Windows 11), I get exception

System.InvalidOperationException: session not created: probably user data directory is already in use, please specify a unique value for --user-data-dir argument, or don't use --user-data-dir (SessionNotCreated)

but the browser windows still opens - apparently in non-automated mode.

I've tried all obvious variants: Specify a different user data dir, specify different profiles, make sure that there is no edge instance running in Taskmanager, try with the "Edge Dev" version, etc.

When I look at the driver logs and run the logged command line in a terminal, I do not see any errors, but also get different behavior.

Dev Machine (working as expected):

Office Machine (does not open in "automation mode"):

What could cause this different behavior?
Are there any command-line options that I could apply to make the webdriver work in all environments?