There seems to be a bug regarding the chance that your horse will gain a skill, the chance is extremely low now. One of the horse i train is a free season T8 (auto learns instant accel, S:instant accel, S: sideways) that is already level 23 but with only 10 skills, it's hard to even gain fore chop! I've been leveling up my T10 Mythical arduanatt and it doesn't learn any skill, i've reset it twice cause it only got 11 skills i think in level 26, used a lot of mount skill change coupon, I hope PA will compensate us for this.

saw this bug in the NAEU forum regarding the horse skill gain bug:
https://www.naeu.playblackdesert.com/en-US/Forum/ForumTopic/Detail?_topicNo=54465&_page=1