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 Open the VRChat SDK in Unity. Run Build & Test Your World or Test Your Last Build. Launch multiple clients at the same time. The second and subsequent clients may remain stuck on a black screen and fail to proceed. 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: Disable debug log output for the client. Launch the first client. Launch the second and subsequent clients. The additional clients will consistently become stuck on a black screen. 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.