Out of date NetDriver despite seamless travel

Hello fellow developers!

I am working on a multiplayer game and currently trying to connect my clients to a dedicated server simply using “open IP_ADDRESS”.
Everything works perfectly in local, but when attempting to join over the Internet, I get the following log on client side:

As you can see, it spams “SetActiveLevelCollection attempted to use an out of date NetDriver: GameNetDriver” until timeout.
All other posts about this issue are either about Steam (which I am not using currently) or seamless travel, which is activated on my gamemodes. I also have a proper transition map set.

There is a temporary fix in the source code of the engine printing this warning (see attached), so I thought about updating to 4.27 (I use 4.25), but this code is unchanged in both versions.

So any idea what could be causing this? Could improper port redirection be the issue?


SoulShards.log (417.9 KB)