My stamina will not deplete when I sprint [KCD2]

Hello everyone, i'm wondering if this is a bug or feature. Of course i'm not complaining as it lets me run infinitely without stop, but it also makes some skill points i invested kind of pointless now (looking at your Ranger's Run).

I'm currently lvl 16, Str 16, Agi 14, Vit 17(+3) and speech 13.

I've tried quiting and coming back: no change. Is it a hidden buff for reaching a certain stat treshold or is it a bug?

Edit: The alchemy skill "Dark Arts Apprentice" seems to be the cause. Between 0 and 4 am it seems my stamina will not deplete while running. I hope this finds someone asking themselves the same question.