Hi
I do not grow masdevallias jet, or, I just accuired one actually, but I remember that I was told that there are viruses doing this to masdevallia plant if the condition is bad for the specie.
My thoughts are the following though:
The heavy spotted leaf, on the right on the first picture, looks like a fungus attack to me. The leafs with a black tip could be salt buildup or possibly high light. The leaf that got dry with out black parts or spots I would say it could be due to high light contitions,you could have dried them out with heat radiation from your T5, even though your air temperature is not exceptional high.
Unfortunate some of these thoughts do not fit with your conditions but may be something to conider
Good luck
/M
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