I have a similar experience..the Hoya shooting star that I have in bloom, it has finished off 2 out of three umbels, then I noticed one of the lower peduncles dried off, so now left with one umbel in bloom and one peduncle still green. Worried that something is wrong, since I have read threads everywhere that hoyas rebloom on old peduncles, I kept reading on and found someone's post that said this particular plant likes it more moist than most, and she mentioned putting her plant's container on water, and the plant thrived even more.
Since our temps here has been really very, very dry and getting hotter too, I decided to step up watering, though not putting the container in water, I think that will be too much. And that slight adjustment worked! The lower peduncle is now setting buds, and not wilting, and upper umbel still blooming well. Learning something new everyday!
