At one time I had about 200 of these in a greenhouse in England,heated to a minimum somewhere below 60 iall the year. It would not be far above that even in summer at night. Leaf drop was not a problem, and believe me when it did occur I hated the sight of bare legs.
I do have a rhrips problem, or maybe more than one,now. There are almost as many thrips species as orchid species ( 19000 compared to 25000) so it seems probable to me that the different feeding habits I see amount to the different behaviour of different thrips species : flowers damaged especially around the edges of the petals of cattleyas, bud blast on cymbidiums so that flowers never open, bulls eye punctures on new cymbidium leaves...
I started again with Vandas, buying what I thought were miniature types after scrapping them all after verysevere over-heating, and they are now getting up to flowering size , and some of the unknown hybrids among them turn out to be large flowered ones after all - but- and here is the point, growingin the same greenhouse as the cattleyas etc which are suffering thrips damage, the vandas are free of damage. And in fact on overa hundred plants none suffer from leaf drop at all.
I think it isyour cultural system generally, and onlywish I could suggest a cure, but I cannot.