There is a backlash test file attached to this post that you can use to help identify/measure the issues:
Another thing to check is the focus lens, make sure it is not loose.
Less likely, but also worth checking, is for any small wobble or front to back pivot movement in the laser head, which can start to happen if the bearings in the x-axis carriage block behind the laser head/mounting bracket are wearing out (just try to physically try to wiggle laser head from to back as if the rail is the pivot point).