Help! Large Black Patches on 2 BLC ShingFong ‘Tian Mu’s

[realoldbeachbum]

I purchased 2 of these orchids 1.5 years ago from Triton Orchids (thru Etsy). They thrived in my environment until 4 days ago. I was on travel for 4 days and returned to large black patches on over half of the growths. The patches are mostly on the tops of leaves, but appear to be bleeding through to the underside on some leaves. None have reached the top of pbulbs. Pbulbs are green & healthy, and 2 new growths have no patches.

From photos on St. Augustine’s website, it appears to be sunburn, but they have been sitting under the same grow lights for the past 1.5 years with no increase in light. The other 4 Catts on the same shelf have no such patches.

What do you think this is? How would you treat them if they were your plants. (I have isolated them.)

All advice is appreciated!