Whenever you log into a server, the game will try to match up an existing character with whatever ID the game client provides. In most cases that will be your Steam ID - but if for whatever reason it isn’t always, then you will indeed see the character creation screen whenever the ID provided by the game client doesn’t match what’s stored on the server. This is at the core of the trick I use to swap and manage multiple characters per account in my tool, as it’s a fairly simple yet foolproof way that doesn’t tamper with any actual gamecode.
So if some or all of your game sessions up 'till now have - for whatever reason - been utilizing “-nosteam”, then you will indeed have to continue to do so. Whether that’s the case and if so how I cannot say, but it would certainly match what you’ve been experiencing.