So here's the bug:
I leveled to lvl 21 in the mid-game using the camp-function.
Later in the game i found the other 2 eggs, so i went to the castle and wanted to know what will happen.
What happened is this:

Yep, all the hard gained exp points are gone!
The results are the following:
- the camp enemies are weak (lvl 1)
- the newer shoppable items are lvl 1
- next lvl up: no, u cant abuse it to gain more skill points by leveling up and so make your character imbalanced powerful (too bad)
So i had to reload and had no more use of the eggs.