I did more digging and it seems that the problem is related to the v1.14+ firmware I upgraded it to (from the Flight Core v2 downloads). For some reason in recent firmware updates it breaks the SBUS input.
I verified this by also upgrading a working VOXL Flight and was able to reproduce the same problem with the upgraded firmware in 1.14 and 1.15.
Any idea why this would break on the latest firmware releases?