I have had this happen a time or two or three. Generally during production runs. It slowed down significantly after I grounded my machine. Grounding your Shapeoko - CNC Machines / Shapeoko - Carbide 3D Community Site
When it happens now I unplug the “brick” transformer from the wall, turn on the machine wait a few min. Plugin and start again. I don’t know why this happens or why it clears the issue. It has solved my issue a time or two or three.
Good luck