pit stops truble

Hi,
during the pit stop, I received the message that my mechanics had lost time with the tires or fuel. I happen at least once per game.
What did I do wrong?

Nothing.
It's just because your mechanics are on level 1 and that's why they might screw up your pit stop. Train them, then this won't happen and they will do faster pit stops.

my mechanics are level 6, but I guess it's not cheap.

thank you!

Seems like you had bad luck. I never had such problems even with level 1 mechanics.