If you're talking about the yellow leaves, some leaves occasionally die. You just cut them off. The rest of the plant looks pretty good to me. Since you had mites, you need to spray again 7-10 days after you sprayed the first time, to kill newly hatching mites. Also occasionally clean the undersides of the leaves with a wet paper towel or soap and water. I often use an insecticide soap to clean the underside of the leaves. Insecticide soap is not a poison but it's pretty good at getting rid of some pests.
Thanks for the advice...I'm actually more concerned about the BPL Golden Peacock in the second photo....the leaves are dying very quickly and it has affected some younger ones as well....attached is how it is starting...
The first plant, I was thinking fungal or viral.
The yellowing could be the result of spraying chemical.
The second plant, premature yellowing and dying of leaves or plants can be due to viral infection, unless watering issues are involved which I don't think is the case as yours is mounted.
If the plant is valuable to you, testing for virus is probably a good idea because you can guess all day and night but not know for sure.
Most likely a fungal or bacterial infection like guignardia or septasoria. Could also be brown leaf spot or brown root rot. Lots to choose from. Find a fungal/bacterial spray and treat promptly. Go to the staugorchidsociety.org website for good information on diseases and cures. One of the best on the net.