I have had a Shapeoko 4 XL for almost a year now and mostly liking it, but I have one persistent issue.
When the machine is off there is a little bit of play in the gantry, the two different Y motors can move independently of each other, so when power is turned on they aren’t always in the same position relative to each other.
This means if I lose power or have to turn it off because it’s about to crash, then next time I try to resume the cut it is always aligned a tiny bit differently and causes alignment issues.
Is this just a limitation of the shapeoko, or do I need to align/tram it better?
I address this on my SO3 XL by pulling the gantry flush against the endplates before powering up — having the consistent starting position seems to help.
A thing to check is that the Y-axis belt tension is even/consistent.
Also check your v-wheel tightness. If the two Y planes are parallel and the v-wheels are tight then it should move in unison even when powered off. Sounds like either your Y rails are not parallel or your v-wheels are not tight enough. As @WillAdams suggested make sure your belts are the same tightness. Move the gantry all the way to one end and put our finger under the belts in the middle to see if they have about the same tension. Lift up a little and compare. The human finger is an incredibly precise instrument.
I have seen posts on the forum about using the Gates Belt Application that you twang the belts and the frequency is analyzed. I have not used that application so not sure how useful it is.