Most likely you activated a repairing ability during your last battle (Repair Unit Module or a special ability that restores a portion of your robot's durability).
At the moment there's no separate graph for the stats that would show all repaired durability points. These points are added to the damage stats right now. Whilst max damage on player's profile shows raw damage only.
NOTE: Skirmish battles do not have effect on player's statistics (as well as rating and task progress).