Back pressure from hyd pump ,look at pump and see if it has a screw in valve or a valve attached the valve is for brake and steering
They will go bad and cause the back pressure on engine causing the issue you have
I would find a part breakdown of hyds
And look for the diverter on some models it looked like a plug that takes an 18-22 mm wrench you unscrew it and take out and replace also check hyd control valve
The control valve has a pressure valve that screws into it that has caused this issue also
Bottom line too much back pressure on hyd pump causing to put engine under strain during start up if engine did start it would most likely break hyd pump or at very least blow line apart