Morning Glory or weeds?
The year before last my morning glories were eaten by this catapillar (attached). Last summer, the never grew back. This year I have something growing but the leaf looks more pointed than rounded. Therefore I can't determine if it's my flowers trying to make a come back, or a weed. The picture with the flowers shows how fullly they once covered my deck railing 2 years ago. Today I only have the 1 measly vine....unless it's a weed, as well as what appears to be new shoots. But unfortunately they're growing in the crack of deck floor "away" from the railing vs close to it.
I'm no expert but I think those are tussock moth caterpillars. I didn't know anything could kill morning glory! The one plant does have more pointed leaves than your handsome patch. But it doesn't look like bindweed to me. Of course, you'll know by the color of the flower. Bindweed has a white, sometimes whitish-pink flower and it is smaller than cultivated morning glory flowers. Also, bindweed leaves are more triangular. So I think you have a keeper.
It appears to be the same morning glory plant re-growing.
The insect pest is 'tussock moth caterpillars'. Do you or a neighbor have a tree overhead or nearby where they could be migrating from to your underlying plants? They can be controlled by a professional applicator (tree service or pest control company) or you can spray a bio-pesticide like 70% neem oil as a repellent or insecticidal soap as a knock down contact spray or combine both in a tank mix.