I put this intermediate temp. Masdevallia medjiana x geminiflora out for the first time this summer. Lots of chlorotic leaf spot. Is this typical for excessive heat stress or is it a good indicator of virus?
I am still waiting on new growths to open up and I have isolated the plant.
Magnesium could be low. My fertilizing frequency schedule has been irratic since July. None of my other Masdevallia are showing anything similar. I'll keep it isolated and pay attention to fertilizer.
Especially if it showed up suddenly when you changed the conditions, I doubt virus. As far as heat goes, different species (and hybrids) can have widely different levels of tolerance. That could easily explain why one was affected and the others weren't.
Try watering a couple of times with plain water containing about a teaspoon of Epsom Salts per gallon. If that is a mag deficiency, it’ll go away in a few weeks.