The removal job is incomplete. All those roots will sprout when the weather warms.
So either remove all greenery as soon as you see it. Then repeat ad nauseum.
Or apply herbicide to all new greenery. Then repeat ad nauseum.

Any and all roots of Ivies need to be dug out or they will sprout new growth. The safest method of removal is to dig. Ivies seem to have an ability to stop the spread of the herbicide, which will contribute to the pollution of your environment, to the roots so often herbicides are not very effective in controlling Ivy.

Ivy "stops" the herbicide because of the waxy coating on the leaves. Apply a wipe-on treatment to newer growth is quite effective. As said, repeat as needed.