The 1.2 X motor is slightly more powerful and can replace the 1.1 motor. You will need to adjust the x motor in Settings/ printer settings. Change Z home offset settings to 10400. That is for the 1.2 motor. But, thats not your problem
To solve the problem you are having, print a piece on each side of the platform (left to right). Now, it should slide the full extent .
When they added dynamic Vat positioning,they added an on/ off setting for it... but that setting in the OFF position apparently no longer turns it off and has been that way quite a while.
What happens is after about 15 minutes, it starts going 1/2 way if you only have pieces on 1 side.
So putting a piece, no mater how small on the other side, will trick the printer into sliding all the way.