Update: Plant looks better than ever probably that heavy feeding yesterday, or maybe the copper spray I don't know exactly what the hell is going on with this if I'm honest but I do think it's fungal

Nothing has spread, so I've only sprayed that one plant which I know is risky but I'm actually keeping a close eye on this for a change

I'll post up pictures if anything changes, thanks again for the help

Edit: to add the affected plant is from seed so it's not a weak drawn-out clone and doesn't appear to be a weak plant; this is a cutting from that affected mother, seems normal too