Hi Bruinsquad,
I'm sorry to hear you're having issues with the eye detect focus on your EOS R6 Mark II. The function on the EOS R8 and the EOS R6 Mark II is the same. Since the sensors are different there can be some variation in how they perform.
The subject tracking and eye tracking are designed to work together. So when the camera is unable to detect the eye it is supposed to automatically switch to tracking the body and then go back to tracking the eye once it is detected. That helps the camera adapt better to subjects if they are turning away or moving quickly.
It would be good to double check eye detect is set to auto. If it is set to either left or right it could make the camera slower to detect a bird's eye since their head can move so much and sometimes only one eye is visible. To do that press the menu button, go to the first page under the AF tab, select Eye Detection, and make sure it is set to Auto.
One other thing to check with something like this would be your tracking sensitivity and acceleration/deceleration tracking. Depending on how those are set it can make the camera prioritize switching subjects or adjusting focus more than may be needed in your situation. Setting the tracking sensitivity more to the negative side causes the camera to prioritize staying tracked on your currently selected subject. Going more to the positive side of acceleration/deceleration tracking can help the camera adjust correctly for subjects that make sudden movements.
Information on the tracking sensitivity and acceleration/deceleration tracking settings are on pages 522-523 of the manual. If you need a copy of the manual it is available HERE. Once you are on the web page click on the manuals button and the one to reference is named EOS R6 Mark II Advanced User Guide.
