Are the Y stepper drive I-parameter adjustable? I printed the dual color example below as is and layer along the Y direction shifted. After I adjusted the speed to be ~25% of normal (randomly picked trial number) the print came out perfect (but slower as expected). I believe the Y stepper may have skipped with higher speed print (100%) and wanted to tweak the drive current to see if any improvement.
@C_U Out of curiosity: in the thread Help, terrible beating noise there are at least two people that got printers with not sufficiently greased linear guides. All linear guide rail manufacturers I know tell you to push grease into the correct holes in the guide blocks - I highly suspect simply putting grease onto the rails as Snapmaker currently suggests would not be sufficient.
Such lack of grease in a linear ball rail guide can result in evil sounds as in the linked thread, but it also may cause the linear guide just to become difficult to move or get blocked for a brief moment when a ball gets stuck due to lack of lubrication - something I can easily see as a cause for a layer shift.
Did you check the amount of grease in the linear guides of your J1 and / or lubricate them?
I had not checked as I am not sure of the correct amount nor which grease is compatible with existing grease. I think grease will help too as stepper will not have to work as hard.
Yes, this is indeed something Snapmaker needs to work on - their current manual leaves a lot to desire in this respect. From what I learned so far, it might well be worth a try to check what a “proper” linear guide manufacturer suggests for for a similar sized version - at least that will be what I will do when I get my printer as soon as I know that it works in general.