[Solved] First layer perimeter and infill out of alignment  

First layer perimeter and infill out of alignment

I'm running into an issue with the right side of the bed that suggests to me that something is out of whack but I can't get my head around what. As can be seen, the fill is out of alignment with the perimeter on the right side of the bed. It's worse the further to the right I print but I'm getting good results of actual objects if I keep them to the left of centre. I appreciate the first layer isn't quite dialled in yet, I've just done a reset and run the wizard again to try and solve the issue but I don't see the point in finessing it any further until I solve the bigger problem.

I've checked the belts, bolts and other obvious things I can think of but I'm struggling to understand what is likely to be root of the problem as this is the same layer. I noticed it while running the 3 x 3 test pattern so simply made my own pattern to eliminate a code problem. This pattern is one 0.2mm layer with two additional instances added in PrusaSlicer. 

The printer is a kit build that I completed about 3 weeks ago, and the problem has probably been there from the beginning but hasn't shown itself because I was only printing small stuff. Where my thinking is getting stuck is surely if there's an alignment issue with the frame the whole shape would be skewed rather than the two parts of the same layer.

Any thoughts?