Coelogyne cristata with fast growing black splotches on leaf tip

[KleioP]

Hi all,

I first noticed these black spots on the tip of one of the leaves of my Coelogyne cristata one week ago (although it could be they were there longer). I cut the leaf well under the damaged area, into the green part, but yesterday I noticed the spots being back (and looking slightly different, now more watery almost). This morning, not even 24 hours later, the splotches are increasing. Any idea what might be happening? Is this what leaf tip die back looks like or could this be bacterial?

One note, because I had spider mite problems I did 3 treatments with paraffin oil (more for prevention, I do not think this plant was infected). The last treatment was a couple of days after I cut the leaf, so could this be a problem of oil entering the leaf at the point of cutting?

Otherwise the plant looks very green and healthy, with the exception of one more leaf that has a black tip (also in pictures).

Thank you very much for your help!