So I rescaped my tank with a new piece of driftwood which was kind of like a mystery piece of wood, I had no idea what kind it was, and it didn't leach any tannins... at all. strange right?
well the next day several leaves on my crypts had withered and melted. and now more and more. But this didn't start happening at all until I put the driftwood in there. could there be some kind of connection between the two...?
You can find out if the driftwood is the problem: Remove the piece, do a large water change and see how the plants are affected.