~1.5 year old indoor avocado plant recently started getting these black spots near the central vein. It's only on the top face of the leaf and only one leaf is affected.
There seems to be no difference in texture on the leaf. besides this spotting the plant is general of ok health.
as seen in the image below, the spotting is only visible on the bottom when light shines through the leaf.
I couldn't find any images of this sort of spotting online so if you have any idea what this might be I'd appreciate it.