Q.Hyacinth bean
My hyacinth bean plant leaves have turned yellow and are falling off. Why?
Yellowing leaves could be watering issues; too much or too little, pests, disease or environmental issues.
Pests can be treated with Neem Oil, which also works as a fungicide.
Hyacinth Bean plants need lots of water, but soil should never be soggy.
The articles below will refresh you on the care requirements.
https://www.gardeningknowhow.com/ornamental/vines/hyacinth-bean/purple-hyacinth-bean-care.htm
https://www.gardeningknowhow.com/ornamental/vines/hyacinth-bean/hyacinth-beans-in-pots.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm