Mane was signed to replace Robert Lewandoski so it is a norm for fans to complain when he is not helping the team to win matches due to his inability to score goals but since they have returned to winning ways, I believe the players will be motivated to put up a better performance in their next matches.
Those fans should also understand that forward position is not his natural position so it will take time to adjust. He is a great player in attack and can help Bayern with great achievements but they gotta give him time to adjust to his new role and tactics that manager is giving him.
Now they have Dortmund next so definitely they needed a win to set things right before facing their main rival in Bundesliga. Should be a tough match so it will be interesting to see how Bayern deals in their next game day after their CL match.