I have a cartesian independent dualX that shows "weird" behaviour as already reported here
At some point during the print, the extruders only move towards their parking position. I have tried with LAZY_DUAL_X_AXIS enabled and disabled and it happens anyway. Suspecting the drivers (RAPS128 on RADDS), I added a DIRECTION_DELAY, but that did not help either. Single extruder print does work as expected, so it is safe to say that is related to dualX mechanics.
I then stumbled upon @Braccoz improvements (aka hidden feature) and tried to go along this path. But same results again. Here is my configuration.h (as .jpg)
Unfortunately, I failed to manually reproduce the behaviour reliably. But printing a dual color benchy constantly failed at the same height / layer. At some point during the print, both heads will only move towards their parking position - e.g. left extruder only moves left, right extruder only right. I suspect that the offsets increment over time and when they reach a certain threshold, they display the errant behaviour.
Will post back if I find a reliable way to reproduce the behaviour - apart from the benchy.