Hi, I was hoping someone would recognize what's on my hibiscus leaves. I've had three large shrubs for years and they overwinter in a very cool part of the house while I'm away at college, so someone else waters them(not often, they get stressed)and I wouldn't know if something has been on them until recently. I just noticed that many of the leaves on one of the three look like most the tiny veins have been scraped or sucked out so the pigmentation is almost gone. I've never seen anything like it before, but I'm hoping it's just something common I don't recognize. Some of the leaves are yellowing as well. There are no bitemarks,insects, or residue on leaves as far as I can see. I'd appreciate it if anyone recognizes what this is, thanks!

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