yellowing oncidium spike and buds

[Jadeco]

The one and only spike on my oncidium started turning yellow at the tip. The 2 blooms fell off yesterday. Not really sure what's wrong.

The root picture is a little blurry, but you can get the gist of things. The roots are overall healthy, especially the bottom ones peaking out from the pot. Some of the top ones are a dark brown, but not dry.

The leaves are perfectly fine, and you can see the spike in question on the left.

Update: the yellow spread more and some browning appeared. I cut the spike above the third node from the bottom. There is a new "branch" growing from the second node.