I'm in the Lower Keys not far from Key West. I have a few dozen species and hybrid vandas outside in a shadehouse.
They get overhead misted 2x/day for 10 minutes, fed weekly, etc.
They all kick off a few leaves every now and then. I doubt it is temp as they seem to do it randomly throughout the year and the lowest we have had here over the past few years is mid 50's and that usually doesn't last for more than an hour.
I've resigned myself to believe it's just something they do because they keep growing and blooming.