How much sunlight does it receive?

The mix doesn't look bad, but perhaps the container is a little large for the size of the plant?

Do you ever fertilize? If so, with what/how much?

Josh

Don't worry, Jan! Your plant won't die. Hoyas are tough and yours still has plenty of healthy vine to work with.

We all experience new vine die-back, which usually happens when you underwater as new growth is still getting established. It is unclear whether this is the case here, or whether it was a mature section that shriveled.

If it's the latter case, the root system may have been compromised due to overwatering (=roots rotted) or underwatering (=roots dried out). Josh is probably right that your pot is on the large side for this plant. I would check the roots and examine carefully for pests. If all looks okay, just be extra cautious with the watering schedule for a while until it turns the corner. Sometimes Hoyas will just start fading, fading, fading though, so if it continues to decline and be problematic, you will have to consider restarting it. There probably isn't a person here who hasn't at one point had a Hoya be a pita for months, chopped its roots off, and had a silky smooth relationship with it ever since.

Best of luck!

Out of curiosity,
how many hours in the day are closed the blinds?