There's something i noticed that happens more often than i would like

Then you die, sometime you're so frustrated by this situation that you're near to tell the Eidolon to end that character so you can start another (one of the main reason of my characters final death i must say).
But despite the frustration you may sometime decide to just go back and give another go to that damned monster despite you know he's back at full health and so will probably kill your character again and you're going to throw your PC through the window.
And then the very strange thing happen : you actually beat the monster in only a few rounds without any kind of difficulty.
As this has happened a lot of time with various characters i am really wondering why this can happen as it can't be coincidence considering how many time that exact situation occured : are the monsters stats re-rolled when you come back from asking the Eidolon ?