Sometimes both of Mereks X and C abilities bugs out. The ability gets a cooldown but no effect for instance. Sometimes he won't jump, sometimes he won't slice. Sometimes the effect happens on the last spot you tried the ability (singleplayer, haven't tried him out in MP yet).
#Merek's abilities bugging out
brazen cradle
shut quest
This happens with Merek, Vizargo, and Aurelia and it happens many times per game. It also hasn't not happened to me throughout a game. It might have happened with Cyrus too but not 100% sure. The other 3 did for sure though (I haven't played Edwin or Aelis outside of campaign). Also singleplayer for me.