When was the last time you gave them plant food? Some form of food, diluted will definitely help.
The other possibility is water. In high heat, water might be evaporating faster causing your plants stress.
I would do this, watch for any bugs (the hole appears isolated, but definitely, keep an eye out). Feed the plants diluted food (any generic food will do, if you are organic, that is fine too, but remember to feed a little at a time), water them and do add mulch, so the pots can retain moisture.
If you live in a very hot area, make sure they get at least part shade for the day. Peppers usually like the heat, but not if it is sustained and very, hot.
Give it a week or two, and see what happens. Usually with food and water, the plants will perk up.