Ok, I missed that.
I tried with 1DX, 1.4XIII, 12mm Kenko, 2XIII, 70-200 F2.8 L II @200mm, still no joy.
Even if I manually focus first and then press the shutter button halfway, it still hunts and is unable to acquire focus.
It is night in Oz, but I switched all the studio lights on (=a lot) and sufficient distance around 10 m (=manual focus works) at a high contrast subject, it still hunts like mad.
I will try in daylight tomorrow morning, but I have little hope.
Anyway, it works in manual mode, so thanks for the the tip !!
Hope this informs