Per few KSP posts (1, 2, 3), this bug is the zero throttle value when transiting from Local Control to Remote Control. This is lethal on RO where a limited number of ignitions are allowed, often with a single ignition.

RO is re-compiled RO 11.5.1 for KSP 1.3.1 (EngineGroupController.dll, UnityGUIFramework.dll, RealismOverhaul.dll)