I have a stock Kingroon KP3s (the one with the linear rails) which runs on Smoothieware. The first dozen prints or so came out fine, but then I noticed ocassionally the print would fail with the extruder simply stopping mid way through the first few layers. No nozzle clog (extruded fine after resetting machine), no skipping steps, no loss of power to the extruder motor (extruder would still be energized and could not be turned by hand), just no movement from the extruder motor. All other axes would continue on just fine. After resetting the machine and restarting the print, everything would behave normally.
This problem became more and more frequent, until now every print has this issue. The extruder always stops mid way through the first layer, meaning I cannot complete any print.
Any ideas what the issue might be, or how to go about debugging?