Afterthought on that, also make sure you go into the Access Control page for that "Hybrid" SSID and try running dual band, even if only temporarily, and see if any devices can see the SSID on both 2.4 and 5GHz channels (or perhaps one but not the other). Wondering if you might have selected 5GHz only and for some reason the 5GHz radio isn't transmitting (perhaps reg domain related) but you should at least be able to see a 2.4GHz signal, manually set it to channel 6 for example.