It was me using the A9 ii, when using slower shutters and continuous burst shooting when you first press the shutter release it creates an initial lag and then it's like you're watching a slideshow effect whilst you're holding the shutter down.
It is a known effect but maybe some people see it more than others, like the tearing effect that have plagued some of the Panasonic cameras, or the graininess when you start to focus on some Sonys
If you don't see it then don't go looking for it as it's a pain
I'm interested to see what the A1 will be like this weekend, I'm going to try all 3 EVF refresh rates, the new frame rate low limit setting (which is supposed to negate the issue) as well as turning off live view setting effect if none of the solves the issue. Lab coat at the ready
On a different note I was looking at your Goodwood photos last night, stunning set
Goodwood really lends itself to great paddock shots doesn't it