Hey Jason,
I agree that this looks like the X-axis continues normally (movement to the left), but Y-axes go their own way, like omitting some of the movement forward.
The connectors (not the controller) are the weak spot on this machine, especially combined with the lack of strain relief on this machine. That’s why I would first check what is described in this FAQ document under point 3). This is the most common cause of such problems.
But also the issue described under point 5) could be the cause: That one of the Y ball screws or both are blocked by wood dust/oil mix inside.
What can also temporarily block a Y ball screw, is if the machine is not accurately squared horizontally. See here for details.
You could also check point 4) (ball screw coupler).
But also finally, and only after having excluded the other points, you could check point 7).
See also the mysterious issue here.
Finally EMI can always lead to strange phenomenons. This is always difficult to track it down, which is why it is good practice to take good precautions here (correct grounding and bonding of all metal parts, use of shielded cables). As for the router, much of its EMI comes from the sparks on the carbon-brush commutators which you cannot prevent by a shielded cable.
My bet would be issues 3) or 5).