Dying Oncidiums? Yellowing, spotting, leaf drop, etc.

[captainbug]

See attached pictures. All are intergeneric oncidiums as far as I know.

I let them dry out between each watering (which is why the soil is dry now). Repotted maybe 2-3 months ago into a dirt-bark mix.

I thought at first that it was just some shock and older portions dying off, but now it is affecting new growth.

I've got some gnats, but aside from that no pests appear to be present.

The one that is completely gone it seems like (left corner of the diamond in pic of all 4) wilted over between last night and this morning, and what I'm holding in one pic is those wilted over leaves that fell out with this soggy rot (which makes no sense considering FULL dry out and no water in 2 weeks). Is this related to the fusarium that killed off my vanda?

All of my phals, as well as one additional oncidium, are doing perfectly fine. Same water, same conditions, same lighting.