A small update:
I found the pin info for the FEM module where the CA antennas connect to from
here (scroll down).
I accessed the FEM module in the passenger foot area and performed a continuity test from the passenger side CA antenna (the working side) to pin 10 & 28 of A173*9B. Did not get any signal on either. In fact, I tested literally all the pins on all the connectors (A173*7B, A173*8B, etc) and got nothing...
I disconnected battery during all of these tests. I double checked all wires and performed the tests multiple times. Anyone has any experience testing continuity from these pins? These results are very puzzling lol. From 2016 onwards, did the pin assignments for the FEM module change? Any common mistakes that people make when doing continuity tests?