s4 rev a wybron scroller problem

Hello ETC..long time listener, first time caller here..

i have 5 s4 revolutions rev A with wybron. one of them only scrolls thru about half the gel string. the same fixture does this on a different wybron gel string as well...

these are in a club a i work at load primarily with high end fixtures, and we got these a few months ago, this problem started about a month later..

any help?

much appreciated.!