Same problem here. When tracking was enabled once via Tobii Game Hub (DCS install dir located inside the app and tracking toggled) mouse look no longer works even when tracking is toggled off.
The reason is HeadTracker.dll inside DCS' bin folder. Tobii copies the file there to enable tracking. Unfortunately once this DLL is present, you can no longer use the mouse to look around.
You have to remove the DLL to get mouse look back.
If sent the Tobii support a detailed bug report and they were able to reproduce it. It's been forwarded inside the company.
FWIW the same bug is present in Elite Dangerous while inside the cockpit. Also headlook bound to an axis no longer works, even when tracking is disabled. The "fix" for Elite is to simply quit Tobii Game Hub (not a real solution). Strangely enough while on foot on Elite you can use the mouse to look around and turn your avatar while also using tracking to look around. So it is possible to use both at the same time.
I hope Tobii fixes this issue, sometime you just want to disable tracking for a minute and use the mouse instead.
PS: Maybe send a bug report to Tobii to make this bug more visible inside the company.
