DRV8426E: The output waveform of PB & PB_N are abnormal

In our case (using TI DRV8426ERGER MOTOR DRIVER IC), there is a transportation problem when feeding feed motor, when printing, the paper got stuck and sometimes rolled back.

per check, the waveforms of PB & PB_N output are abnormal. but PA & PA_N seems normal.

1. Is there any sequence or timing requirement on VM on/off and  signals ?

2 Are there any directions and suggestion for debug ?

e2e.ti.com/.../SCH_5F00_WAVEFORM.pptx