Any chance of a pic? Am guessing folks will be better able to suggest diagnosis if they can see the problem area.

I have Hoya polystschya but not the IML 1410 collection of this species. The new leaves are matte while still growing but mature to a shiny finish. Are you saying that the leaf was already mature but then changed to a mette finish? Did the cells collapse and for large sunken patches? What about the colour of these areas? A photo would be very helpful as this could be many different things.
Did you change anything about how you care for the plant? Did you move it to a sunnier spot, outside, altered its care in any way?

Bacterial rot is most often a wet rot. Fungal rots can be either but fungi often start in one area and then work outwards and often leave the leaf yellow or brown.

Mike

PG, thank you for your prompt response. I will work on a photo.

Dr. Mike, thanks as well. Very reassuring that what is wrong with 1410 is likely not contagious.

The leaves are glossy and the sunken spot was matte and wrinkled. Your description of collapsed cells is helpful and likely, accurate. There was no color change - all areas are a nice green. The only change in cultivation is that the sun is now substantially stronger than in the winter and occasionally, I leave the window open. But, again, there is no leaf discoloration to suggest that the sun is too strong. Do you think the sunken spot is a reaction to increased light intensity? And although I cannot recall letting it get bone dry, is it possible that this species could react this way if I inadvertently let it dry out too much? I have been resisting watering it more as its leaves are so succulent and I do not want to overwater at this juncture. Perhaps I'll move it to a more shaded spot to see if that helps.

Just when you think you've got hoyas figured out...

I do find it strange that the leaf remained green even on the affected areas. You may not have had to remove the leaf, if it were cell collapse due to whatever reason, it would most likely not have been caused by a pathogen. Is there any chance that you got water on the leaf during the brightest part of the day?
This Hoya does like to dry between watering but during active growth it also wants more water to help develop those large leaves. Winter time is the time to let it dry the most but right now it much more capable of dealing with extra water. Either way there is very little chance that the problem was due to insufficient moisture.

Mike

Just throwing this out there.....Scale infestation? Or the beginning of? Or a few drops of water that had fertilizer mixed with it?

No, not scale, and likely not a drop of fertilizer or water - the area was about the size of a quarter.

I will isolate the plant and if the second leaf worsens, I will try and post a photos. Thanks to all who posted!

Lisa