What could be causing this

[OnefinityCNC (Onefinity Support)]

Most likely this:

Red Bushings on Motor Coupler. What is it? (Do not throw away) FAQ

The Red Bushings (shaft coupling) on the motor coupler are not packaging. They are an integral part of the coupler and required for the machine to move correctly. Flexible shaft couplings are used to connect the shafts of a stepper motor and the driven load or mechanical system. They allow for the transmission of torque while accommodating misalignment, reducing vibrations, and protecting the motor and driven components. Without these red bushings, the machine will not cut correctly as there w…