On the leaf of your Panda Plant, I see what appears to be a couple of bits of perlite and to the right below the perlite, I see a couple of small spots that just looks like the plant tissue has calloused over, which could have been caused by small holes from insect bites or mechanical damage from bumping, etc. If it isn't spreading, I don't think it's anything to worry about.
Is that last hoya photo the same plant as pictured in your first set of photos? The leaves look to be yellower which may be a watering issue.
