Could this be gamma difference?
No, gamma the same (2.2).
Were you using contrast in corona postproduction tab? It got reworked in A6, so it is possible you need to re-adjust your contrast settings
Yes. But if I insrease contrast to 4.8 in A6, colors is very different.
My settings

increased contrast to 4.8 in alpha 6

Colors in alpha 6 are not accurate. And the situation does not change white balance :(