Not sure if this may be causing your issue, but I had my X-carve suddenly leaving the path and doing unwanted moves in the middle of projects. However when doing an air run with the spindle off, it always worked fine. Whenever the spindle was on, it hardly completed any project correctly. I am using the lowcost spindle by the way. Increasing the drive current of the stepper motors did not solve the issue.
Upon coming across a few comments mentioning spindle noise interfering with the stepper drivers, I hooked a 5µH LISN into the supply line of the spindle to check conducted noise with a spectrum analyzer. The conducted noise level that I measured was extremely high. Far beyond the limits to pass any EMC standard.
Next I built a simple filter consisting of a common mode choke with 330nF capacitors at each side. The common mode choke is a salvaged part, a 30mm diameter ferrite toroid core with 2x 15 windings. This filter, in series with the spindle supply, inserted close to the spindle, significantly reduced the noise, except in the range somewhere below 100kHz.
After inserting the filter, the issue with my X-Carve disappeared.
I am about to order a few common mode chokes from Digikey to further reduce the noise in the low frequency range. I will then post the schematic/BOM in this forum