After the game it analyzes for something like 5 seconds, so it's very superficial. The "game review" analysis takes longer, so the engine has more time to reach a high "depth" so moves that were previously counted as blunders aren't anymore... but it could also happen the other way i.e. the number of blunders may increase.
A similar thing happens when you set the depth higher and run the analysis again. Your score of 67.9% may go a little higher or lower and the number of blunders / inaccuracies / etc can change.
This is a game I just played.
Chess.com says I had 0 mistakes and 6 blunders.
But upon clicking "game review," it says something completely different.
It says I had 4 mistakes, and no blunders.....?!?! This is profoundly confusing.
Can someone better explain this to me?