L6491 half bridge gatedriver is destroyed regularly
Source of my problem is dv/dt and parasitic capacitance Cgd (gate drain capacitance, sometimes named Crss in datasheets). Nice description of this problem is here Cgd dv/dt problem in synchronnous buck

Solution - slow down high side mosfets, 0 Ohm shutdown gate resistors (only fast diode in series),  use RC snubber.