Too much rain
My morning glories have been subjected to an unusually rainy season. The vines are getting brown and growth is thinning. The leaves and flowers seem ok at the top of the plant. Can I save them?
Morning Glory can tolerate many soil conditions but soggy soil can be a big issue. The roots can perish from root rot.
I would trim it back and see if it can recover.
You may want to use Neem Oil on the plant to help it stay pest and fungus free while it is stressed.
Here are a few links for you.