The big issue here is Mourinho's expectations VS Pogba's "intentions".
Recall back the recent comments by Mourinho and all the comments by players who have and are working under him. All basically said one thing, Jose have high and many expectations of 'em all. Mourinho's style is to challenge his players to become better and better. Not every players are in tune with this. He's a hard trainer, and treat every players the same, which can both be a good and bad things in player management.
In his eye, Pogba is not yet the finished article, there is room for growth. His recent comments about the B2B thing and Pogba's position reflects this. His persistence in playing Pogba in midfield two is also a hope of him fulfilling that potential. Here lies the problem.
For a manager of this calibre, Mourinho, he's not that blind in seeing Pogba's inconsistencies. In his first season, he did turned to midfield three after Pogba's bad performances, to retain balance in midfield, but reverted back to midfield two after Pogba "settle down". In this second season, after recruiting Matic who can solo-mid in some games, he then revert back to "train" Pogba in the midfield two, trying to fulfill his potential.
Pogba is a good professional, but everyone knows his character orientation, which reflects and expressed from his football. He himself made comments of his preferences in playing football. Freestyle, freedom, attacking, stylish, entertaining, more on-the-ball football. So, at first, it really is a mismatch with Mourinho's disciplinary and hard approach. Pogba is a happy-go-lucky kind of person, who prefers to play freely. That's just his nature. A total maverick.
After his amazing career with Juventus, Pogba doesn't strike me as a player attempting to improve even further, or at least his motivations for that is no longer that much. His next objectives are more on to winning the big trophies playing for Manchester United. Doesn't strike me as a player seeking to be the best of the best, therefore no need for more improvements, but more of a player satisfied with his footballing capability, which is that top class.
Football skills = Technical skills + Physical skills + Creative skills + Mental skills + Tactical skills.
While everyone knows Pogba have top class technical, creative and physical skills especially, his tactical skills is truly lacking, but no worries, it's coach-able. That's the only thing helding him back in midfield two (plus motivations) - the know how and when to position himself in different phases during matches. Instead, he prefers to go all-out attacking playing freely, stylish football. Understandably, this coincides with his free nature. Still, it's hard to accept his somehow effortless attempts during defensive phase in many matches this season, that costs us points. It's as if the addition of Matic makes him thinks he should no longer try.. and just focus on playing freely. I don't blame him though.
The possible solution here is either...
(1) Mourinho stops coaching him to become a more complete midfielder, which I believe he is pondering, after his public comment in planning to get a midfielder this upcoming summer. But if he do so, then it is saying Pogba is done, can never be the all-time best midfielder. Admit it, many of the best midfielders can play in midfield 2, so why not Pogba? It'll be the most thing which downgrade Pogba - "he can't play in midfield two, so how is he the best". Scholes and Pirlo did it. Of course pairing with a more defensive midfielder, but still they play well compatibly. Now, Pogba have Matic, no more excuses.
(2) Pogba realize this and fulfill his possible "real" potential, to be a more complete midfielder, than what he already is. Dispel the myth of him can't play in midfield two. So what if he's the best in midfield of three, everyone knows that, Pogba knows it, even I'm sure Mourinho knows this. But can he play in two?
Interesting not many people can see the bigger picture of this dilemma. As long as both Mourinho and Pogba doesn't fall-out and retain their professionalism, we'll reap the rewards.