What about mites? I've had mites that leave marks, but no webs, so there could be mites even if u don't see the typical "web" signs... But I dunno? This is kinda wierd :/
Did the mites you had leaf these kind of marks on the leaves??
I have been wondering if that is also a possibility because I read about mites that are smaller than red spider mites, which I can see with my naked eyes with no problem.
It is just one leaf from last year though. The plant grew another leaf after this "bad" one and that newer leaf is solid green.