One thing immediately jumped out - the NGINX image has not been updated [for years](https://github.com/signalapp/Signal-TLS-Proxy/blob/ac94d6b869f942ec05d7ef76840287a1d1f487f9/nginx-relay/Dockerfile#L9). In fact, NGINX 1.18 is so old that it has gone end of life for [a year and a half](https://endoflife.date/nginx) as of this writing.
My Docker Compose setup can be found [here](https://github.com/tommytran732/Signal-TLS-Proxy). I have also fixed the missing `:Z` flag for mountpoints and and dropped privileges to reduce the attack surface. I made a couple of pull requests for these changes, but Signal is being very slow on reviewing and merging them, so... yeah.