Unanswered Robo seems to lose track of Y axis while printing

Ive kept a running log of problems i have had with the printer as well as fixes, date oriented, but this one has me at a loss. ive printed many hours, and never experienced this issue until i updated the firmware in matter control from 1.4 to 1.5. The Y axis seems to jump/jog forward a couple steps and mess up the print. it will continue printing like nothing has happened, but on flat vertical surfaces is clearly noticeable as an edge is formed that is not in the slicer. I have never experienced an X axis jump, only Y. Any one else and possible cause fix, my guess is that a driver is under/over powered or something in the new G code. I have no experience editing G code but may need to to fix this problem. AS you can see in the pic this is suppose to be a flat wall it has jogged a step and is now out of alignment both in the front and back.

 

You might want to check and see if the small gear attached to the shaft of the Y stepper motor that drives the belt is tight.

 

Belt and pulley are tight, (could belt be too tight causing an issue?) i regularly check all the hardware, level the bed manually, grease moving parts etc. The symptom is not frequent enough, its kind of a rare occurence but has happened about 3 or 4 times out of maybe 35 prints, but i am starting to become hesitant to print larger prints now. I think its either a firmware, software/slicer issue or driver. Have you seen a driver go bad exhibit missed steps before failure?