Y Axis scaling problem

First time here.
Looking everywhere for help and readed a lot of stuff on the web. I’ve got a Chinese Red/Black 9060 100W with Ruida RDC6442S0B. I have working with it for a month without any problems. X/Y axis were calibrated on RDworks. Until yesterday, where i found out that i have problems with Y axis.
When i make a square 10/10 cm it almost perfect (x=9,96cm and y=10,04cm), but when i want to make a square 3cm by 3 cm my result is: x=3,01 and 2,81cm! What can cause this problem? HELP!

Got new Info about it.
When i make a square 3x3cm and push Frame button on Ruida controller. Laser will position it self at the beggining of the shape. When i press start it will cut perfect. But if i want to make another shape near the first one (so the laser head need to travel) it makes X size bigger about 0.2mm then Y size.

Most likely a mechanical problem. X axis backlash

Any idea how can i get it fix?