Black spot & burned leaves, please help!

[mBluebear]

Hi guys,

I have some questions about my orchid.
I have an orchid which all the leaves were sun burned 2 years ago (no leaves left). Then, magically it's still alive and produces leaves. However, it's very slow. I saw some black spot and part of the a leave was burned. However, this leave was under some other leaves, I don't think that's sun-burn. This orchid was placed close to an orchid which was infected by snails. I repotted them last Saturday, but saw no snail in this orchid. Is it doing ok? or it was infested with something?

Thanks