kurotori
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
  1. Open the VRChat SDK in Unity.
  2. Run Build & Test Your World or Test Your Last Build.
  3. Launch multiple clients at the same time.
  4. 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:
  1. Disable debug log output for the client.
  2. Launch the first client.
  3. Launch the second and subsequent clients.
  4. 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.