〇 Environment

OS: Windows 11 Pro 25H2 Build 26200.8457

Unity: 2022.3.22f1

VRCSDK: 3.10.3

〇 Summary

When performing local world tests using Build & Test Your World or Test Your Last Build, launching multiple clients simultaneously may cause the second and subsequent clients to become stuck on a black screen.

Launching clients with a delay between each instance can partially mitigate the issue.

〇 Steps to Reproduce

〇 Additional Reproduction Conditions

Based on investigation, this issue appears to be indirectly related to log output.

The issue occurs consistently under the following conditions:

〇 Possibly Related Issue

A potentially related issue, also suspected to be caused by log output, was observed:

When two clients are running in a local test and are in the same world, performing a rejoin from one client causes VRChat to crash.

After this occurs, VRChat will continue to crash consistently when rejoining the same world, even when running only a single client.

This issue can be resolved by deleting the log files in the following directory:

%HOMEPATH%\AppData\LocalLow\VRChat\VRChat

〇 Suspected Cause

It is likely that a deadlock or similar resource contention involving log files is occurring, causing clients to freeze or crash.

〇 Expected Behavior

All clients should launch and enter the world normally when running multi-client local tests.

Rejoining a world should not cause crashes regardless of log file state.

〇 Actual Behavior

The second and subsequent clients may freeze on a black screen when launched simultaneously.

Under certain conditions, rejoining a world causes VRChat to crash persistently until log files are deleted.

〇 Notes

This issue significantly impacts local multi-client testing workflows and should be addressed with high priority.