I have done that already yesterday after the first print going wrong. Then the second print went wrong, then the testcube printed correct. this morning first goes right, second fails.
I lubricated again, let the machine cool down(see if that has any effect). Printing another sample gave same result.
The X and Y motors feel equaly hot at the end of the print. I can still touch them so I would guess they are 40-50 C (60 C is maximum what one can hold)
Looking at the mechanics the only other thing I can think of is that the upper belt connection of the X motor (all the way in the upper right corner at the back) might be slipping.
So I took the smallest hex-key and turned both hex-screws tighter. One seemed to give a little.
I am test printing now to see if this resolves the problem.