pi 3 B+ power module not working.

[ionut]

I have the pi 3 B+ working with OP v3.  
The power module will not shut down the pi gracefully. I have setup everything per the docs: 12v to board and another 12v to switch.
When I cut the power to the switch the pi powers off instantly. If I bring gpio21 down by touching pin 39 to 40 the pi power down gracefully, so that works. I setup the pins thru the settings app per the docs.
Is there something else I should be aware on the pi3. 
Thank you,
RJ

[ionut]

I have the pi 3 B+ working with OP v3.  
The power module will not shut down the pi gracefully. I have setup everything per the docs: 12v to board and another 12v to switch.
When I cut the power to the switch the pi powers off instantly. If I bring gpio21 down by touching pin 39 to 40 the pi power down gracefully, so that works. I setup the pins thru the settings app per the docs.
Is there something else I should be aware on the pi3. 
Thank you,
RJ

A bit of a follow up.
Measuring the voltage on pin37(gpio26) during bootup sequence I get 3.2 volts at the beginning of the bootup and then it drops down to between 0 to 2 volts jumping all over the place. Applying 3.2 volts to pin37 from pin1, I can initiate the bootdown sequence from the switch. So I narrowed it down to pin37 not having the required 3.2 volts to keep the power module enabled during bootdown.

[Adrian]

That seems to indicate that the Raspberry Pi is not taking control of the Power Off pin. So the issue is likely with the configuration. Can you post your settings in OpenPlotter and the relevant lines in /boot/firmware/config.txt (or /boot/config.txt if it's an older version of Raspbian)?