Last week on the Friday morning update, I had 1 kill not counted toward rank.
Saturday all I flew was one attack mission with six kills then I ping shot myself accidently. These all recorded accurately.
Today/tonight (Sunday) I flew two bomber sorties (six because of formations with no kills that I'm aware of) and two fighter sorites (3 kills on each, one ditched and the other disco'd on an arena re-set).
Now I have 5 kills not counted toward rank. The three kills that I had when the arena re-set didn't change my K/D, K/S, K/T or Kill Hit % at all so I suspect none counted toward my rank (a B-17, a 190 and a P-38 all killed while in a 190A-8). I have no idea where the other "not counted" kill came from but I suppose it may have been Friday night (I did a few vehicle and fighter missions and it seemed all my vehicle kills didn't record either... 5 in a Tiger).
It seems something may be wrong as I usually check (and record) stats after every sortie although I miss recording one here and there.
[EDIT] I just checked and I'm not showing a disco for the arena re-set either.