I can't say that I've ever seen this before. At first look, I thought some type of bug, snail maybe. But it also looks like some type of chemical damage.
I know this isn't any help.
Have you sprayed it with anything or had any kind of spray around it?
Hopefully someone will recognize these spots and help you out.
Sure looks like scale damage to me. See if you can find little white or grey spots on the leaves or rhizomes. They will be small sort of hard things that you can scrape off with your finger nail. Let us know, as these guys can be hard to controll. Good luck.
I had something similar. I was afraid it was mite damage, so eventually after safer soap, neem oil, etc, used Bayer 3 in 1 several times and isolated plant from others, (It was on a phrag). Now new leaves are fine and so I think it must have been a bug. Betty
Thanks for the ideas. The photos dont show how to lesions are pitted rather than raised. There are no encrusted scales seen. The backside of leaves are pretty clean. Ive isolated the plants and will treat with soap.
my guess is scale damage. they won't go away but if the scale is gone you won't have any further damage. they are tenacious so you may have to respray with insecticide or insect soap for a few cycles.