I have done some more testing with the A1 on firmware 2.01
With the bare 600GM I am seeing no issues.
With the 600GM+1.4TC I have instances where it will not re-focus (not dependant on spot or zone focus) but I am not at all sure that this is firmware dependant.
I had a day out where re-focussing seemed sub-par, but it is spring here, with many light green fresh leaves on the branches, that let quite a bit of sunlight through.
It may well be that these are too low contrast for the mirrorless af system to "see".
When I keep the AF engaged and move the lens slightly, it will in a few seconds re-focus.
The thing that makes this slippery territory, is that a dslr like the D500 would jump into focus in such circumstances without issue, but mirrorless AF is different and still surprises me at times.
So my summary is that I am not going to list this as firmware issue, but as a mirrorless AF issue. When there is clear enough contour or contrast, I see no issues with AF.
Eye AF seems quite ok.