A customer asked this common question, so I will answer the question in a REPLY post:
"The LTspice model indicates that PWRGD is not correct when the LT3086 SHDN pin is low. Is the model correct?"
PWRGD on the LT3086 is only active if IN and SHDN are high. I have worked on this issue before and never concluded the LTspice model was wrong. You may be able to invert PWRGD as done by the LTspice simulation I uploaded. I show the circuit and the simulation results in the image below. Alternately, some customers have added their own comparator and reference.