[GH-ISSUE #16136] issue: Intermittent "Unexpected token 'd'" error when streaming responses (v0.6.15) #17791

New Issue

GiteaMirror · 2026-04-19T23:40:30-05:00

GiteaMirror commented

2026-04-19 23:40:30 -05:00

Originally created by @dalaoyang on GitHub (Jul 30, 2025).
Original GitHub issue: https://github.com/open-webui/open-webui/issues/16136

Check Existing Issues

I have searched the existing issues and discussions.
I am using the latest version of Open WebUI.

Installation Method

Git Clone

Open WebUI Version

v0.6.15

Ollama Version (if applicable)

No response

Operating System

CentOS Linux 8

Browser (if applicable)

No response

Confirmation

I have read and followed all instructions in README.md.
I am using the latest version of both Open WebUI and Ollama.
I have included the browser console logs.
I have included the Docker container logs.
I have provided every relevant configuration, setting, and environment variable used in my setup.
I have clearly listed every relevant configuration, custom setting, environment variable, and command-line option that influences my setup (such as Docker Compose overrides, .env values, browser settings, authentication configurations, etc).
I have documented step-by-step reproduction instructions that are precise, sequential, and leave nothing to interpretation. My steps:
Start with the initial platform/version/OS and dependencies used,
Specify exact install/launch/configure commands,
List URLs visited, user input (incl. example values/emails/passwords if needed),
Describe all options and toggles enabled or changed,
Include any files or environmental changes,
Identify the expected and actual result at each stage,
Ensure any reasonably skilled user can follow and hit the same issue.

Expected Behavior

Streaming responses should be handled gracefully and rendered progressively in the chat UI. The frontend should not crash when receiving malformed, partial, or incomplete data: lines from the SSE stream. Instead, such chunks should be ignored or logged, allowing the session to continue without interruption.

Actual Behavior

Intermittently, the UI throws a SyntaxError: Unexpected token 'd' when parsing streamed SSE responses. This breaks message rendering and requires a page refresh. The issue does not happen consistently.

Steps to Reproduce

Deploy OpenWebUI v0.6.15.
Connect it to a self-hosted LLM backend with streaming enabled (stream: true):
- DeepSeek-V3 via SGLang
- Qwen3 via vLLM
Start a chat session in the UI and send a prompt (long or short).
Observe the streamed response — most of the time it works.
Occasionally, the UI crashes with:
This seems to happen randomly and cannot be consistently reproduced, but it occurs in normal usage conditions.

Note: The error appears to be caused by a malformed or partially received SSE data: chunk being passed to JSON.parse().

Logs & Screenshots

This error appears intermittently during chat message streaming. It seems to occur when the frontend attempts to parse a data: line from the SSE stream as raw JSON.

Additional Information

No response

Originally created by @dalaoyang on GitHub (Jul 30, 2025). Original GitHub issue: https://github.com/open-webui/open-webui/issues/16136 ### Check Existing Issues - [x] I have searched the existing issues and discussions. - [x] I am using the latest version of Open WebUI. ### Installation Method Git Clone ### Open WebUI Version v0.6.15 ### Ollama Version (if applicable) _No response_ ### Operating System CentOS Linux 8 ### Browser (if applicable) _No response_ ### Confirmation - [x] I have read and followed all instructions in `README.md`. - [x] I am using the latest version of **both** Open WebUI and Ollama. - [x] I have included the browser console logs. - [x] I have included the Docker container logs. - [x] I have **provided every relevant configuration, setting, and environment variable used in my setup.** - [x] I have clearly **listed every relevant configuration, custom setting, environment variable, and command-line option that influences my setup** (such as Docker Compose overrides, .env values, browser settings, authentication configurations, etc). - [x] I have documented **step-by-step reproduction instructions that are precise, sequential, and leave nothing to interpretation**. My steps: - Start with the initial platform/version/OS and dependencies used, - Specify exact install/launch/configure commands, - List URLs visited, user input (incl. example values/emails/passwords if needed), - Describe all options and toggles enabled or changed, - Include any files or environmental changes, - Identify the expected and actual result at each stage, - Ensure any reasonably skilled user can follow and hit the same issue. ### Expected Behavior Streaming responses should be handled gracefully and rendered progressively in the chat UI. The frontend should not crash when receiving malformed, partial, or incomplete `data:` lines from the SSE stream. Instead, such chunks should be ignored or logged, allowing the session to continue without interruption. ### Actual Behavior Intermittently, the UI throws a `SyntaxError: Unexpected token 'd'` when parsing streamed SSE responses. This breaks message rendering and requires a page refresh. The issue does not happen consistently. ### Steps to Reproduce 1. Deploy OpenWebUI v0.6.15. 2. Connect it to a self-hosted LLM backend with streaming enabled (`stream: true`): - DeepSeek-V3 via SGLang - Qwen3 via vLLM 3. Start a chat session in the UI and send a prompt (long or short). 4. Observe the streamed response — most of the time it works. 5. Occasionally, the UI crashes with: 6. This seems to happen randomly and cannot be consistently reproduced, but it occurs in normal usage conditions. Note: The error appears to be caused by a malformed or partially received SSE `data:` chunk being passed to `JSON.parse()`. ### Logs & Screenshots This error appears intermittently during chat message streaming. It seems to occur when the frontend attempts to parse a `data:` line from the SSE stream as raw JSON. <img width="2137" height="446" alt="Image" src="https://github.com/user-attachments/assets/db59f949-e254-4298-b41b-cfd93d832bbb" /> ### Additional Information _No response_

GiteaMirror added the bug label 2026-04-19 23:40:30 -05:00

GiteaMirror closed this issue

2026-04-19 23:40:30 -05:00

GiteaMirror commented

2026-04-19 23:40:32 -05:00

@tjbck commented on GitHub (Jul 30, 2025):

Unable to reproduce, please check your websocket config.

@tjbck commented on GitHub (Jul 30, 2025): Unable to reproduce, please check your websocket config.