Without a picture of the damage I cannot pinpoint whether it is an insect or disease (especially since it has returned). Examine the plants to see if the insect is tunneling into the leaves (leaf miners), eating the leaves (slugs, cucumber beetles, earwigs, etc) or it could be a virus causing the damage.

While I wait for a picture or two, look for slime that would mean slugs are present, look for chewing insects, look for aphids, which usually means ants and sticky honeydew. Go out at night to see if you have cutworms or earwigs as they are nocturnal feeders.

If you can find any insects and take a picture of it too, that would help me come up with an identification and a suggestion for a deterrent.

I look forward to hearing back from you.

The damage looks like some critter is cleanly biting off the edges of the leaves. Do you have fencing around the area to keep out rabbits, deer, squirrels, possums or racoons? If no fencing, you could use row covers to protect the plants from browsing animals.

If you have fencing, make sure the narrow spaces go all the way to the ground so no small animal can go under or through the fence.

There are deer repellents available but not for use on plants you plan to consume.

If this advice does not help, I can pass the question on to another expert.