Hi
My problems with X and Y movements is during a print after a wile the X or Y will be misaligned with many mm(up to 10mm).
It is not the belt that’s are over stepping, I have marked the wheel and belt.
The settings for movements it changed to Accel: 4000 (was 6000), Vmax X and y is now 100 (was 150).
It is not related the position of the print on the board.
Tjellvar
This could be for a lot of reasons
Check the pulleys for the belts and the ones on the motors.
Make sure the screws are tight.
You should also check the alignment.
You can find more information here
http://www.k8xxx-3dprinters.crimed.be/w/index.php?title=XY-Carriage_Alignment
lubrication is always good idea.
Had issues while not properly lubricating
The problem is solved.
The rods going throw the printer head needed more oil than I expected.
This is a new printer and the surface of the rods are a little ruff, they will be better after some use.
You can see it buy the black stuff on the rods.
great,
I have had the best experience with the PTFE oil.
Silicon will not work, since per specification it is not made for metal on metal lubrication.
That was, what I figured out and I was reading the spec after that experience 
The problem was not solved after oil on the rods passing the printer head, I needed also put some silicon on the rods for X and Y movements. Those going throw the plastic pats. I have also add 1mm rubber gasket above the nut on the 50mm counter slinked screws holding the printer head. This will mage the extruder to be able to move up a little if it hits some obstacle.