Wow....I'm sorry to say I have no idea what that might be? Hopefully, someone here can diagnose it for you. Can you post a picture of the front of the leaves? I might be able to ID the hoya at least...

Do you see any bugs or pest on the plant?

Good luck!

here is another pic, kinda tricky with the light. the leaves have some white specs on them. i reinspected and don't see any pests or any other similar leaves. there was a few leaves that are sort of faded and starting to go soft, but in each case there is a new growing tip right in the same area.

It looks to me like the leaf may have just been damaged. I've found a similar pattern after I've rapped something against a leaf, kind of like squashing it. It doesn't usually appear right away, but within a few days. Could it have blown in the wind and smushed up against something?

Denise in Omaha

it def could have got blown around, its just hanging on the porch. the effected leaf was toward the end of one of the hanging vines. the vines seem to have a mind of their own moving all over the place never where i want them, i will probably put on a trellis when i bring in for the winter. i was thinking about this second pic last night. in the background there is a sick rhododendron that i dont pay any attention to, its part of the landscaping and i rent at this location. the leaves are yellow and im thinking has a similar pattern on the back of the leaves, i will have to investigate when i return home...i had just changed the hoya location to where it was in contact with the rhod leaves.

Your Hoya looks like Carnosa...it looks quite healthy and very dark green. I bet if you gave it a little more light (not direct sun) you will buds soon. Denise explanation sounds right, I'm sure its fine. Just keep an eye on it and see if it appears on any other leaves...