Might be early damage starting.

When I zoom in on your first picture, I think I see the discolouration going over the vein just a little bit. If that's the case, it wouldn't be nematodes. Try the water test to check for presence. I used a lamp to backlight the water (and a magnifying glass)...easier to see the tiny little things. I hope it's not nematodes Windymess. Maybe it's bacterial leaf streak. There's info on that problem in the Articles section on Library home page. Maybe it's just the plant starting to wind down?

I was freaked out too when I found nematodes in one of my hostas. I put that hosta in the trash, poured boiling water over the soil, planted a rock. All I know is that rocks don't look as good as hostas.

I should add that I'm not an expert by any means and actually don't really know what's going on.

Not nematodes. Bug bites or frost damage or some minor injury to the leaf now generating some necrotic tissue in the heat of summer.

I’ll definitely read more from the Library and see if I can check these lesions more closely!