What’s killing my plant?

Hi everyone, I've been growing peppers since last year, and lurking this sub in the meantime.

The peppers (early Jalapeños) I've grown in my office had brownish/spotted leaves at the end of the season, and looked very unhealthy.

I've overwintered one of them, cleaned the roots as well as I could and repotted it in new soil. It started back nicely, sprouting new leaves and flowers.

However some of the new leaves show stigma that I saw last year and I'm getting worried that whatever issue was there last year is back with a vengeance.

Fungus gnats are in force this year, but i'm trying to deal with them with sticky traps and nematodes. Last year covering the soil with sand finally ended my problem with them, however the leaf stigma persisted, so I'm guessing this issue is not fungus gnat-related.

Any of yous have an idea what's wrong with my plant and how to remedy it and not to spread it to my new sprouts?

A thousand thanks!