Is this Y-axis backlash?

My infill does not reach the perimeter. This effect is most pronounced where the perimeter is parallel to X-axis and this effect is not present where the perimeter is parallel to y-axis. Interesting to note that all perimeter layer are consistent (on top of each other) and all infill layers are also consistent (have the same borders) but infill simply does not reach the perimeter, in some cases by about 2mm.

Any one seen this before and can tell me how to fix t?

Thanks ahead.