Websocket connection issue with Plugin in Unreal when using Gamelift Anywhere on dedicated server

Hi! I've tried to follow these guides: https://docs.aws.amazon.com/gamelift/latest/developerguide/unreal-plugin-anywhere.html for setting up Testing on a local machine and https://docs.aws.amazon.com/gamelift/latest/developerguide/integration-engines-setup-unreal.html for generally setting up unreal correctly. I'm using Unreal Engine 5.1.1 Source together with the GameLiftPlugin for Unreal Version 1.0.0, which contains the GameLiftServer Version 5.1.0.

I have successfully started and tested GameLift Anywhere with my project on two different, local machines running Windows 11. But anytime I try to start the Server on a dedicated server, I get the following result:

Connection to GameLift websocket server failed. Retrying connection if possible.
Connection to GameLift websocket server failed. Retrying connection if possible.
Connection to GameLift websocket server failed. Retrying connection if possible.
Connection to GameLift websocket server failed. Retrying connection if possible.
Connection to GameLift websocket server failed. Retrying connection if possible.
Connection to GameLift websocket server failed. See error message in InitSDK() outcome for details.
1001[2023.12.28-15.46.50:614][  0]GameServerLog: ERROR: InitSDK failed : (
[2023.12.28-15.46.50:614][  0]GameServerLog: ERROR: Handshake with GameLift websocket server failed. Please verify that values of ServerParameters in InitSDK() are correct. For example, process ID needs to be unique between executions, and the authentication token needs to be correct and unexpired.

I have tried running the server on two different hosters (Hetzner and Strato) on both Ubuntu 22.04.2 and Windows Server 2022 Standard Edition. The servers are equipped with the necessary hardware to handle the game server.

I have made sure, that all values of ServerParameters in InitSDK are correct. The process ID is unique every time. The authentication token is updated in a script before running the server and is correct and unexpired - I validated it using the AWS Cli.

I have tested the websocket connection and am able to connect to the websocket using TELNET. I have temporarly completely deactivated all Firewalls on each system to test for any issues there.

I am aware of this very similar issue: https://repost.aws/questions/QUhBkyXMcuQ26sKPa2Z2aDIw/how-to-debug-issues-with-gamelift-anywhere-initsdk But I was able to start the game server on my development machine without issues and additionally have checked every parameter multiple times for issues.

I am also aware of potential issues when building the server SDK with an OpenSSL version that is incompatible to UE5.1.1, but I have checked multiple times and made sure that the SDK was built with the compatible OpenSSL 1.1.1n. The libcrypto.so.1.1 and libssl.so.1.1 or equivalent for Windows have been shipped accordingly with the project files.

I'd be incredibly grateful for any help I can get. I'd also be grateful for anybody that can confirm Gamelift Anywhere is working for them on their own (non-EC2) dedicated server, just so I know that it's possible to run it.