Mane and Kane are both very similar types of strikers, so it's certainly not because Mane wasn't comfortable in the position and so couldn't be brought into the game properly.
However, you do hear rumors from the fanbase that point to your statement that Mane was/is not comfortable in the team. Mane also showed at his previous clubs, especially Salzburg, how perfectly he can score goals, so I hardly think that he has suddenly forgotten how to play soccer.