UDP hole punching in python, works locally but not through AWS

I'm trying to implement UDP hole punching so that I can connect 2 clients together that are not in the same network without the need to portforward. I'm using the top answer in this question as my basis and it works if I run the clients and the server on my local machine (both clients get the "hello" response).

Now I've made an AWS instance that is running the server and opened the ports on it so my clients can connect, however when they've received the ip + port for each other they seem to not reach (they get the response "peer: x.x.x.x yyyy", but not the "hello" response). What am I missing in order to make them capable of communicating? even if both clients are on the same machine it still doesn't work, it only gives the correct response when using the local host (127.0.0.1) for both the client and the server.

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