I have had this issue with my jade plants for several years. All leaves develop a scaly texture after a while. New leaves regrow green and healthy. Some smaller leaves quickly turn silver and just fall off. All of my jade plants have this, but none of my other succulents seem affected. It also doesn't kill the plants, they are all several years old.
At first, I thought it might be sunburn since I have them under a grow light. But then the pattern on the larger leaves almost looks like something is eating through them. In addition, most images of sun burned jade plants I found online look a little bit different (the patches seem to be rounder and have a different texture).
Could this be some sort of fungal infection?
I found this old reddit thread which seems to be about the exact same issue. However, the OP never found the underlying cause.
Looks like fungus infection. Isolate the plant and remove the affected leaves.
I'm wondering whether this could be due to too high humidity
Regardless of what it is. Quarantine the plant. I had a similar issue and it spread to two other plants.