Firstly, we are told that Dr Mann was the best of all of them and he knowingly went to that planet that it might very well be the end if the planet was unsustainable.
Since the planet was indeed a failure, why would he transmit incorrect data. The reasoning that he was desperate to see some human faces seems incoherent.
Secondly, knowing that the planet was a failure and with the available resources all of them could very well return to earth or go to plan B. If he was so interested in living, then he could have gone along Cooper to Earth. Killing the other guy through the bomb in the robot and killing Cooper seemed illogical to me.
Thirdly, how is he able to go to 'Endurance' that too before Cooper and Dr Brand? She picked up Cooper through her spaceship, but exactly from where did Mann get his spaceship?
Fourthly, why does Mann even want to go to Endurance? What are his intentions? Does he want to go back to Earth or is he interested in completing plan A on his own?