Phoenix/Plug connection issues

We’re currently hosting an umbrella app on Heroku that has a proxy application powered by Plug (using Plug.Cowboy) that forwards requests to the appropriate Phoenix endpoint. We recently started running into H18 (Server Request Interrupted) errors. I’ve provided Heroku’s description of H18 errors below.

The backend socket, belonging to your app’s web process was closed before the backend returned an HTTP response.

We just started seeing this error without any code changes. We’re at about 31% memory consumption so it shouldn’t be a resource issue. It almost feels like we’ve hit some sort of threshold. I’m curious if I need to adjust cowboy’s or ranch’s config or something?