Why can't I lan with myself anymore?

I used to play garry’s mod all the time with my sister. What I’d do is log both my computer and the family computer on steam, both on my account, in offline mode, and have my computer start a listen server and have the family computer join via LAN. This used to work. Now I get “STEAM validation rejected” on my family computer, and “S3: Duplicate client connection: UserID: 3 SteamID: [steamid]” in the console on my computer.

Is there a way to fix this? I already tried sv_lan 1.

Edit: I solved it by typing “connect [localIP]” in the console instead of joining from the menu.