To me it looks like the arms might have been bent/rotated slightly which causes the imbalance.
Try to see if the arms can be bent/rotated at the joint and try playing around with their positions.
It also looks like the chain can slide horizontally within the shackle, possibly you could balance it out a bit there as well.
Alternatively, if the metal is magnetic you could try buying some small magnets and try balancing them out like that.
Looks like all the arms are there, and none are bent.
Looks like the electric wire coming down from the ceiling is interfering with the chain, preventing the chain from hanging freely. The wire and it's insulation may be too stiff, or the wire too short (perhaps due to the side loop used to raise the fixture)