We need to see a close up picture of the underside of the leaf. There are two possibilities:
- overwatering can be caused by lack of drainage, lack of light or just too much water
- spider mites can cause old leaves to drop and they like ivy. Identification would be small grains of salt on the underside of the leaves and webbing
If it is spider mites control with 5 ml dish soap to one liter of water. Good coverage is essential and hard to do the way this plant is growing. You can dip a cloth in the soap and water solution and rub the top and bottom of every leaf. Rinse with water after a minute or so and repeat at least twice more at five day intervals.