In my experience, it usually flashes a brief message telling me why it is disengaging... I've seen messages for:
1. Exceeding 85 mph
2. Glare on cameras
3. Tunnel Ahead
4. Hands not on wheel
The most common one I see is some variation that the cameras are partially blinded. Either by glare or a little rain.
The second most common one I see is that the road doesn't match what it has in its database due to construction. It happens at the exact same location repeatedly.
