In order to try to remedy this situation, I've fertilized everything with fish emulsion. The plants seem to be getting better, or at least they've stopped their downhill slide.
The aubergine and Mad Hatter pepper look terrible.
The two bell peppers also look sad. I've never had an insect problem on them until now. I guess it proves that insects are attracted to sickly plants.
These are both Athena melons. The first one is in the raised bed, the second one is in the ground. They were the same size when I planted them.