There is a GRBL configuration $1 that sets the idle delay before stepper motors are disengaged. Setting this to 255 keeps motors always enabled. However, xTool firmware prevents any GRBL changes so this option won’t be available to you.
However, if this is the case I suggest you sort out mechanically what is causing the areas that bind. You really want this to be consistently free moving. Even if you try to work around the issue it will likely cause other artifacts that aren’t immediately apparent.
The motor shouldn’t be shutting off during the burn, only at idle time so not sure why this would be the case. Are you sure the slipping is in the motor and not along the roller?