My endorsement level drops when I leave a game after it says VICTORY/DEFEAT before the POTG. It has happened multiple times, where I am lvl 4 and continue to get endorsements (at least 1 or 2 per match) then it just drops to 3. The only change I make is I leave the game before the POTG. According to this old post that is not supposed to happen Overwatch Forums
That post was made before the endorsement system was introduced.
1-2 endorsements per game is not really enough to maintain a level 4 reputation. Well we don’t know exactly what’s needed i can tell you it’s still not enough.