Thank you for reaching out to find out what's going on with the Boston Ivy on the retaining wall behind your Townhouse.  There are a few things to look at for a proper diagnosis.

Why Are Your Boston Ivy Leaves Turning Brown?

If your Boston ivy leaves are turning brown, it’s usually a sign of fungus. The brown spots typically develop in the middle of the infected plant’s leaves. They may even combine to form bigger patches of dead tissue. Tiny black fungus spores may be present as well.

• Brown spots on Boston ivy vines usually indicate a fungal infection.
• Don’t let the leaves get wet when you water your vines.
• Mulch the area around your vines.
• Trim infected leaves immediately.

Trim off infected leaves immediately and spray the vines thoroughly with a copper-based fungicide. When watering your vines, don’t let the leaves get wet. Instead, only water the ground. Mulching around the area where your vines meet the earth can prevent fungus spores from being thrown up during rainstorms.

Other causes may be 

• Japanese beetles eating Boston ivy leaves in spring.
• Spider mites devouring Boston ivy grown in hot, dry areas.
• Brown leaf spots ringed in black are a sign of fungal infection.
• Too much fertilizer can cause a boom in Boston ivy growth, followed by wilting.

If left unmanaged, each of these can be Boston ivy killers. However, with the right pesticide or fungicide, you can battle back insect invasions and disease. If your Boston ivy was overfertilized, simply stop fertilizing and your plant should rebound.

https://peppershomeandgarden.com/boston-ivy-problems/

Otherwise, Boston Ivy is a relatively low maintenance plant and resistant to many other challenges.

https://plants.ces.ncsu.edu/plants/parthenocissus-tricuspidata/

I hope I've answered your questions.  Please free to reach out again with further questions.