EOS R6 Mark II Back Button Focus, ONE SHOT vs Servo

[carl_schnurr]

I have an R6ii and set up back button focus a while back with Shutter button assigned as Metering Start, and AF-ON button as Metering and AF Start.  I usually shoot in SERVO focus mode, but I noticed some strange behaviour.  When I did try ONE SHOT focus, it never seemed to engage ONE SHOT.  The focus square was blue not green, and it behaved as though it were in SERVO. 

I just assumed it was some detail about the focus that I just didn't understand and continued using SERVO exclusively.  I recently had some time to investigate YouTube etc, and couldn't find anything specific about this.  I recognized that it made more sense AF-ON button set to AF Start on detected subject, not Metering and AF Start.  

Making this change fixed my issue and changing from ONE SHOT to SERVO is toggling the green/blue focus square as I'd expect. 

This was quite unexpected and I repeated it back and forth and verified it wasn't something else I changed in between.  Can someone explain why this happens?

[carl_schnurr]

I have since tried using the ONE SHOT and its still not acting properly. The single point focus doesn't stay within the point and jumps around. 

I don't think AF Start on detected subject, I couldn't find an AF-ON button in the button option icon list 

[carl_schnurr · Accepted solution]

Solved my own problem.  At some point in time, I had modified some of the detailed settings in the Metering and AF Start including setting AF operation to SERVO,  and Whole Area Tracking ON.
When I reset AF-ON button to Metering and AF Start and change revert the Detail Set to Default, it all seems fine.

I do like to go deep into the camera menus to play around a bit, and often forget how to get everything back.  I'm sure its a common problem