Have people really not worked it out yet that it's personal with Pep against Jack? He played great against Forest and was then immediately dropped again. No player can keep their spirits up when treated like that.
Jack also always does best when he gets a run of games but Pep is determined not to give him that even though people like Walker and Gundo are getting loads of minutes.
Doesn't matter how Jack trains or plays, it's clear at this point Pep wants him out. Manchester City may as well be called Guardiola City at this point because apparently Pep can do no wrong.