I think randomness is good, it creates good replayability as it makes every play slightly different. However, for the grass level at least, I thought that having unsymmetrical spawn of the boxes was slightly unfair at first because P2 immediately gets access to 1 of the box, but P1 has to jump to higher platform to access the 2 blue boxes. Furthermore, most of the times, the 2 blue boxes spawn at the 2nd/3rd highest of the platforms.
On the other hand, considering that the player can fall "endlessly", it could be argued that the P1 can immediately reach those boxes if they know how to fall properly & immediately reach the top platform too. So, now thinking about it with this mechanic, it was probably a small issue.
Castle stage was fine though.