Hi Mark,
There are two things you can try that may help,
- grounding the Shapeoko: there is great video from @LiamN in this thread. You’ll want to actually check continuity between your spindle body and the shapeoko’s ground.
- running the spindle power cable away from the other Shapeoko cables. But I suppose you already did that and used the drag chain where the router power cable normally does.
And then there is the hit and miss approach to use different outlets for the Shapeoko and VFD