Most likely your Y axis is missing steps at the start of a travel move. So you need more motor torque or less acceleration.
Those motors are rated at 2.0A, which is almost double the current you can get from most plug-in drivers. So with RAMPS and plug-in drivers, you won't be able to run them close to maximum torque without the driver overheating.. That leaves reducing Y acceleration as your best option. Or switch to a board with integrated drivers that can be cooled properly.