It is not an easy diognostic. Could be too much water, not enough water... Could be that the transplanting damaged the fine root system, and a root fungus is taking hold. In this case, watering in a fungicide might be beneficial.

Looks like earwig or pill bug damage on the leaves, not slugs. There are poisons that you can sprinkle around the plants to help lower the populations of pests, if you would like.

You should trim off any damaged leaves and the bottom branches, disposing them away from the plants. I would suggest fertilizing the plants with a basic time-release tomato fertilizer, and sprinkle Epson salt around the root line to help the plant take up the nutrients.