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.
Mane and Kane are not similar, Kane is a striker and Mane is a left winger.
Mane profile and
Harry Kane profile have descriptions for their positions. Mane appearances show he has very little matches as a central forward or as a striker and majority of his appearances is as a winger.
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.
I just read news that Mane said he felt very sick when many rumors about him and he will leave Bayern Munich soon. Mane is able to score goals and at Liverpool, in his last two seasons for them, he scored many goals.