Looks like it's over watered, but maybe someone with more experience with this particular plant will chime in

I don't think it is possible to over water these since they grow stream side on stilt roots when they have to. A plant rooted in a heavy potting soil that is kept wet might look like this. When grown outside they generally like well draining soil.
It looks like the plant is out of nutrients. This could be because the plant needs to be repotted or it could be an insect is sucking the life out of it.

If it just needs repotted, that is easy to fix.

Look up chlorosis and see if that might apply.

Also, look at the roots. Anything like white fuzzies down there? These plants also get scale, although I don't see any on this one.

I'd agree that the problem is in the roots. Either too wet, too much salt build up in the pot, or some sap suckers on the roots. These plants often grow as epiphytes on other trees, or as lithophytes on rock faces. They get a lot of water from their rainforest environment, but it drains very fast and there's good air circulation around the roots. They don't have a high mineral nutrient requirement, but a little bit helps.

-"A plant rooted in a heavy potting soil that is kept wet might look like this."-

Thanks for your help. All three of you mentioned too much water, and now remembering that I had transplanted this one into a larger pot about a month ago. So it is not root bound. But, I used MG potting soil with moisture control, and... kept it watered. Duh. Of course when it started looking sick I gave it more food and more water. Lately I've been letting it dry out.

Yes, it seemed to do better when I "forgot to water it."

The new leaves sprouting from the bottom is a good sign.