Unit set bonus

Can someone explain or help me out I have all four pieces of elder set but only getting it 3 set bonus instead of a 4 set bonus. The gun is not registering part of the bonus

The new NA-exclusive version of the Elder Rifle is not compatible with the Set Bonus; you can check this yourself by clicking on the Rifle and going to the "Confirm Set Effect" option.

@AndrlCh so I went home and check I have three other pieces and only getting this 2 set bonus is there a bug with the elder set do you know of