Sony a9 focus issue

[bnorthr]

I just bought a used Sony a9 (the 2017 "mark 1" version, with the latest firmware) and I've hit an issue with focus tracking. I'm using high-speed drive mode, "AF-C" continuous focus mode, "Tracking: Expand Flexible Spot" Focus area, and back button focus. When I hold down the focus button it begins tracking as expected, but when I press the shutter button without releasing the focus, the lens immediately de-focuses and all the photos in the burst are ruined. This only happens when the shutter is electronic. Anybody seen this issue before? Perhaps there's some setting I need to change to correct this?

 

[jvo]

ah, the nostalgia of the analogue world... remember when the advice "needs a cla" fixed 90% of the problems? in the 21st century frontier i guess it's "replace the chip"?

i hope someone has some better advice for you...

jvo