hello KratinaK83
It seems some sort of submarine or leaf miner.....
Good luck
Elo

This is most likely a fungal infection, perhaps bacteria. Are there many leaves affected?
If your plant has been wet and in cold conditions this is likely the cause. Can you tell us what may have lead up to this.

Mike

Not too many but I have two plants sitting next to each other and both plants have developed a few leaves like this. I first noticed it about 3 weeks ago. The weather has been getting colder but it hasn't been more damp than usual. It seems to start near the bottom of the vine and work its way up. On the first plant I trimmed off that vine and I haven't seen any more leaves like that but on the other plant it seems more arbitrary, not isolated to single vines. I don't see any insects nearby and the soil doesn't look any different. if it is a fungal infection, how do I treat for that? I would say so far maybe 12-15 leaves have been affected and I've b been trimming them off as I see them.

Fungal spores are everywhere but are usually not a problem unless the right conditions for their growth are available. Can you tell us about how you were caring for the plant. Are you growing it indoors or out? Have you been misting the foliage?
This is not an insect so no need to worry about that.

One thing that really helps to prevent these types of infections is a fan to keep the air moving in the room your plants are in. I notice that some Hoyas seem to resent the change in seasons and when it gets cooler and less sunny they can develop infections. I had a rather large Hoya drop about 1/4 of it's leaves but it stabilized after a while. Try to keep the plant in good growing conditions, that means giving it enough light and being sure not to keep the potting mix wet if it's cold.

Fungal infections can be treated by using chemical fungicides or natural products that are anti-fungal. Cinnamon made into a paste with water works well and you can try this on any newly diseased leaves as you see them. Garden sulphur is another product but when the whole plant is affected then a systemic fungicide is probably best. A wettable powder such as Captan would also work but be sure to read all info if using chemicals as some are quite toxic to both you and the environment if not used properly.

Mike

The plants are sitting near a south-facing bay window. I water the plants about once a week and I don't mist them. The plants haven't been repotted anytime recently so they're pretty rootbound, which I hear hoyas like, but I think they both could use bigger pots for the size they are. I haven't been fertilizing them with anything and I keep them indoors. I live in chicago so any time after september I wouldn't keep anything outdoors.

I did start noticing this right around the seasonal change for the colder - about 3 weeks ago when we started needing jackets the soil didn't seem like it was drying out as fast as it had been and then the leaves started popping up with those weird indentations. I've been cutting them off and disposing them as I notice the spots. I haven't been keeping the house very warm.

Hoya carnosa is ok with cooler temperatures but I suspect that your schedule needs to be adjusted to suit the seasons. Water when the potting mix has started to dry out. If you are using a dense potting mix such as plain potting soil problems will be more likely. If you repot add some orchid mix with bark and perlite etc, this will help keep the roots healthy and prevent soggy conditions.

Mike