Problem with local multiplayer

[FruitMaestro]

Operating System

Windows

Description of bug

I would like to be able to start and connect two instances of Minecraft on the same computer. Is UltimMC5 able to do that? Tried with 1.16.5 and 1.18.1. Using both local and ely.by accounts. The result was the same.

Steps to reproduce

1. Starting Minecraft
2. Singleplayer
3. Create New World
4. Open to LAN
5. Start LAN World
6. Starting second instance of Minecraft on the same computer
7. Multiplayer
8. Join Server
9. Logging in...
10. Failed to login

Suspected cause

No idea

This issue is unique

• I have searched the issue tracker and did not find an issue describing my bug.

[MenacingPerson]

You have to use different accounts

[FruitMaestro]

You have to use different accounts

I'm using different accounts for both instances.

[nfrno]

Same issue as OP.

MC: 1.18.2
UltimMC: 0.6.14-custom
Microsoft OpenJDK: 17.1

Two Windows 10 machines with two unique Local accounts
Running instances via Launch Offline
Single player world, opened to LAN
Server is visible from 2nd PC

Joining leads to timeout after "Logging in..."
[Server thread/INFO]: com.mojang.authlib.GameProfile@28583272[id=<null>,name=myName,properties={},legacy=false] (/192.168.1.5:55531) lost connection: Timed out

Curiously, joining works from 3rd machine running ExtremeLauncher 3.9.5.0 with log entry:
[User Authenticator #1/WARN]: Authentication servers are down but will let them in anyway!
[Server thread/INFO]: myName[/192.168.1.6:55159] logged in with entity id 854 at (9.5, 66.0, -6.5)

[Marcelo20XX]

Same problem as OP, LAN is not working, tried to play with my sister in another city via Radmin, tried with a friend with a second PC connected via LAN cable and finally tried to connect with two copies of the entire folder with the client downloaded and with two different MineCraft accounts on same PC, not working in any of the cases

[maxvalit]

Same problem. Trying to play via LAN, Windows host and OSX client
P.S. running on a local account

[lucksma96]

Same problem, but I'm using Hamachi. Most of the time it fails with Disconnected, but sometimes it's with Timed out.
Funny thing is, I'm able to see the server as a LAN World, it shows how many people are connected and the pings work.
Local account as well.

[aeroncastle]

this is not a clone of that bug

[mariotacke]

Did you ever figure this out? Got the same issue.

[Marcelo20XX]

I switched to PollyMC because of this issue... sadly that project got its issues too, mainly drama between the devs and collaborators...

[mariotacke]

Gotcha. (How) were you able to create offline accounts without first adding an official account?

[MenacingPerson]

Gotcha. (How) were you able to create offline accounts without first adding an official account?

PollyMC =/= PolyMC

https://github.com/fn2006/PollyMC