Did you perhaps change settings or upgrade the firmware in your Orbi recently?
Sometimes it’s the opposite and advanced or beta firmware features on the Orbi might be keeping it from connecting at 5Ghz where it would before.
Diego
I’m not sure what changed, but I messed with the settings on my wireless card in the advanced settings in the device manager (they were at what they’ve always been before) - when I get home I’ll look to see exactly what I changed - I changed one that had the option of wireless 802.11 a/b/g to just a/g or something. At that point it connected always at 5 GHz. There was another setting that specifically disabled 2.4 GHz and I tested that separately, and that also worked. I think something on my wireless adapter is a little messed up.
I just use separate SSIDs myself, that way I know for sure what band I’m connected on (also for a while my TV didn’t play nice with 5Ghz, so it was handy to be able to force 2.4).