“Invalid session”

What the message establishes: the server could not accept the session credential your client presented. An expired or replaced token is a common possibility; switching accounts, relaunching, service trouble, or a server/proxy verification fault can all contribute. The message alone does not prove the server is healthy or identify which component failed.

The restart order

1. Quit the game and the launcher completely — closing just the game window often is not enough.
2. Start the launcher fresh and launch the game from it. This normally refreshes the session credential. Try the server again.
3. Still kicked? In the launcher, sign out of your Microsoft account, sign back in, and launch again.
4. Close other copies of the game or launcher while testing; concurrent or recently switched sessions can complicate which credential is current.

What it is not

Usually this is not a reason to reinstall, and it is never a reason to enter your password anywhere except the launcher’s official sign-in. If the error persists across several unrelated servers after sign-out/in, session-service or account trouble becomes more plausible; if it persists only on one target, that server, proxy, DNS path, or route deserves investigation. Gate HD-1 requires reproduced evidence before this desk labels any one cause definitive.

Different message? Back to the desk or the username-verification page.