There are lots of insects and diseases that attack bean plants. The bacterial wilt disease causes young plants to wilt during the warmest part of the day. The disease cannot be cured so uproot and destroy infected plants. But yellow leaves could also be whitefly. Shake the plant and see if specks of white fly from the plants. Control whitefly with insecticidal soap every 2 to 3 days for several weeks. It could also be a root problem from a mole, vole or nematodes. It does look like some white blotches are on the green leaves in the picture. Leafminers leave tunnels or blotches on the leaves. Remove and destroy the infested leaves and cover with agricultural fleece to keep these flying insects from landing on your plants.  To positively ID what is causing the problem you may need to use a magnifying glass to look for mites, miners or leafhoppers or uproot a plant and check out the roots. Nematodes leave roots that are gnarled with root knots. Sorry I cannot be sure of what is causing the problem but with more clues I might get closer to solving this mystery. Keep growing, Marianne Binetti