Found the problem with the motors releasing. The TFT35 firmware has a configuration.h that has the following default content …
//===================================================
/**
- Start/End/Cancel G-code - runs after a print starts, ends, or canceled.
*/
// Start G-code
#define PRINT_START_GCODE “G28 XY R10\n” // Raise Z 10mm before homing X & Y
// End G-code - run this G-code after finishing print
#define PRINT_END_GCODE “G90\nG1 E-4\nG92 E0\nM18\n”
// Cancel G-code - run this G-code after canceling print
#define CANCEL_PRINT_GCODE “G28 XY R10\n” // Raise Z 10mm before homing X & Y
//======================================================
There is an unwanted M18 in the end gcode to disable all steppers. I’ll try to fix that tomorrow but it looks like the culprit.