No idea why, but it is always adviseable to cut the white leaves off. I left some on my H.Holliana not knowing, but they never turned brown like this. When the plant didn't grow past that point, I investigated and was told to clip them off, so I did out of blind faith. So, perhaps the reason is that they zap energy from the plant that would otherwise go into new growth. As far as I know, this only happens with varegated varieties of hoya.
Christine

I have some white leaves my Krimson Queen, but I've left them on there and so far haven't had any problems. One vine is nearly all white. The leaves from the ends on back as far as I can trace them (it's a big plant and all the vines are entangled) are white, but doing fine and growing. I have had green leaves turn brown and wrinkly like the white ones in your pics, but I think it was because I let the plant stay dry too long in the winter.

I don't really know why yours are turning brown. I like the white leaves on mine, but if I ever think the plant is suffering, I'll certainly remove them. I hope someone with more experience/knowledge will come along and give you some answers.

Thanks for your answers!

Christine,
Where do you usually get your hoyas? (I am in Toronto)

ema

Ema, does your hoya get exposed to direct sun light? The white leaves are more sensitive in regards to sun burn due to their coloration. I wouldn't worry too much about it if it's only happening with some of the white leaves.

Milan

Milan, this one is on the south windowsill but, 1.there is another building in front of the window 2.on the right there is a huge tree - shade comes like around 2pm or earlier.
If I count again the frames of those small square windows I would say it is OK for krimson queen. As I am not the expert, I will keep an eye on it.

Thanks.