Masdevallia's leaf problems

[tweakerbee]

I've been growing Masdevallia's for several years Masdevallia's.
But now almost all have the same problem the same problem.

It start with the blackening of the leaf tips at the back of the leaf. (picture 1)
Then the leaves turn leathery after that they turn yellow. (Picture 2 and 3)
Some leaves will curl up.
After that te leaves drop and the plant dies. (picture 4 and 5)
The plants keep producing new leaves.
However, these are smaller and fall off before they mature.

I grow them cool in a greenhouse.

I need some help with this before they all die.