I'm having issues with my ground forces STO PD firing at incomming missles.
Alien race is set to hostile.
My Racial Tracking speed in 4000
Incomming missles are 15.5 km/s
Gaus Cannon twin turrent point defense - ground forces elements present.
Targeting mode set to point blank.
But nothing happens.
Am I missing something?
Just to be absolutely clear - When you say nothing happens, you mean that the missiles slam into the planet uninterrupted yes? In the context of PD nothing happens sounds like the best possible outcome 
Yes, Point defense doesn't fire. Incoming missiles pass through the PD range and hit my ground forces.
Are your STOs ordered to fire in point defense mode on the STO Targeting tab of the Ground Forces window?
Yes they are in PD mode, tested different modes.
If I set them to fire at ships, they fire at ships.
I checked the Sqlite DB and the formation element actually is assigned as "Point defense".