That's just what happen's with the unequal setup period.
Having rise joints just makes it worse because they done have the "give" that rubber bushes do.

It all happens because you have 2 different length arms wanting to travel a different path, technically arc.
Pretty much like having a 3 leg race with your mate, 2 minds, 2 wants and 2 decisions that will take 2 paths.. Ie they fight.

The only way you can get rid of this problem is go equal length, period!

Get a protractor out and a piece of paper, leave the pin in the same point, draw an arc, then increase the length of the protractor and draw another arc..
See how they are both different... That why I mentioned a 3 leg race..you now have 2 different actions, but coupled together by 60kg of steel!
Something has to give, and it's always the weakest link... Spot welds on the chassis near the mounting points.