Error message in initial example during GRF forecast

I using GaitNormal_ 1 in FullBody_GRFPrediction.main, but a warning will appear.
WARNING(OBJ.MCH.KIN6) : Interface.any(215) : GHRot : Close to singular position : Orientation close to Gimbal Lock, i.e., first and third axis of rotation being parallel.
I would like to ask how to eliminate or solve this warning.