I noticed this a while back but always forgot to mention this.
SXP is divided amongst party members as it should.
The problem is that the SXP is divided even when the party members are not on the same screen screen.
The off screen party members are not getting the divided SXP either
So all of that SXP is lost.
Example.
-Player 1 and player 2 are in a party
-Player 1 kills a monster that usually yields 20 SXP but only get’s 10 because of the party.
-Player 2 does not get the 10 SXP taken from player 1 because he/she is not on the screen with player 1 at time of kill.
The 10 SXP that would have been awarded is gone. 
Does the same happen for EXP? I have not checked yet…