Digging more into this.
Found a VIN from a 2015 FiST with nav and compared it to my 2017. Which most likely would've been OP's year.
You can see in the catalog they have two different harnesses that I hovered over in the antenna picture near the bottom. My VIN actually has a splitter for the Nav, other one doesn't.
Then going to the module page, mine showing not equipped but 2015 is equipped on the "19A366"
This must have something to do with it. Again, I haven't actually checked when my sharkfin was plugged in to see it I had nav but if it wasn't in the antenna I think I should have nav, even with the antenna unplugged.
Only thing I can think of is that little box that is on the splitter harness in the picture for my 2017 and that is NOT on the 2015 harness acts as a GPS module when plugged into the antenna, then the antenna just amplifies the signal. That could explain trahma's problem in this thread since he has a 2016 and a 2016 is like mine, unless he had a separate problem, as he did not report back after plugging back in his OE one.