Handicap was set to automatic. I was a 6k playing with white against a 5k with black. Game info showed handicap: 1, and indeed no handicap stones but komi reduced to 0.5.
I think this can happen if color is not also set to automatic - since this is a private game, it must have been a custom challenge, in which that’s possible to do. E.g. if your opponent was set to play black explicitly, but handicap was still auto, I think this would be the result.
That’s a good guess for an explanation. I definitely have not consciously set the color though. And I think the chances that I accidentally did that are very slim. No way for me to check that now unfortunately.
I left the color setting untouched. (Possible accidential misclicks aside.) Actually I think I never touched that setting since playing on OGS.
I haven’t created games since and the defaults when creating a new challenge now are:
handicap: none
komi: automatic
color: automatic
Which seems to indicate the settings are not kept, since I did choose handicap automatic for that game. Or I mistakenly did not set handicap to automatic, in which case the reduced komi we got would need an explanation.