みしゃ（misyaguzi）
Summary
If an OSCQuery-enabled app on the same PC is already advertising when VRChat starts, VRChat discovers it during startup, before login, and fails with a NullReferenceException while creating the OscClient. No “VRChat is going to send data to …” HUD notification is shown. OSC data is still delivered to the app (avatar parameters and /avatar/change arrive), so only the client setup or notification step seems to fail.
If the app is started after VRChat has finished starting, it is discovered without errors and the HUD notification appears.
Environment
  • VRChat 2026.4.1-1931-68b4616cf3-Release (Steam), Windows 11
  • OSCQuery app on the same PC, advertising _oscjson._tcp and _osc._udp on 127.0.0.1 (python-zeroconf / tinyoscquery)
Steps to reproduce
  1. Start an OSCQuery app that advertises an /avatar endpoint (e.g. /avatar/parameters/MuteSelf).
  2. Start VRChat with OSC enabled.
  3. Watch the HUD after logging in, and check the output log.
Expected
The app is registered and the HUD notification is shown, the same as when the app is started after VRChat.
Actual
No HUD notification. The output log shows this during startup (while the login UI is being created, before authentication):
```log
Debug - Advertising Service VRChat-Client-XXXXXX of type OSCQuery on 53316
Debug - Advertising Service VRChat-Client-XXXXXX of type OSC on 9000
Debug - [Behaviour] creating login UI
Debug - Found new OSC Service: <app>:<id> at 127.0.0.1:63269
Debug - Found new OSC Service: <app>:<id> at 127.0.0.1:63269
Debug - [Behaviour] authenticating
Debug - Found OSC Client of type 0
Debug - Found OSC Client of type 2
Error - Could not make new OscClient: Object reference not set to an instance of an object.
Debug - Found OSC Client of type 0
Debug - Found OSC Client of type 2
Error - Could not make new OscClient: Object reference not set to an instance of an object.
```
Frequency
7 out of 7 launches with the app started first. 0 errors when VRChat was started first. In that case the app was discovered about 2 minutes after startup, and the notification appeared.
Notes
  • Discovery happens about 1 second after VRChat starts its own OSCQuery service, while the login UI is still being built. Something used when creating the OscClient (possibly the HUD or notification system) seems not to be initialized yet.
  • Similar log line, different cause (remote PC / request failure): “Osc being discovered on non-local pc” and vrchat-community/osc#169(https://github.com/vrchat-community/osc/issues/169).