OpenClaw version: 2026.5.3-1 (2eae30e)

Channel: webchat (Control UI / dashboard)

Severity: High — assistant replies silently disappear from the UI

Bug Description

In the OpenClaw Control UI, every time the user sends a new message, the previous assistant message disappears from the chat window.

• Disappeared assistant messages do NOT reappear (unlike Control UI chat flickers sent user messages, they disappear briefly then reappear #66207/Control UI: Sent message briefly disappears then reappears (sometimes stays hidden) #67412 where they flicker back)
• User's message history is fully preserved, unaffected
• Refreshing the page does not restore the missing assistant messages (unlike Control UI: Messages disappear during tool execution #37083)
• The assistant messages still exist in the backend session JSONL (confirmed via sessions_history tool)

Steps to Reproduce

1. Open Control UI (http://127.0.0.1:18789)
2. Send a message, assistant replies normally → assistant message is visible
3. Send another message → the previous assistant message disappears from the UI
4. Repeat: each new message causes the previous assistant message to vanish
5. End result: UI shows only the current user message + latest assistant reply; all prior conversation is gone

Expected Behavior

All assistant messages should remain visible in the chat window persistently, and should not disappear when new messages are sent.

Workarounds Attempted (not resolved)

• Set agents.defaults.blockStreamingDefault to "off" (from [Bug] Webchat: previous assistant message disappears when next message streams (blockStreamingDefault conflict) #33641 workaround) — did not fix
• Gateway restarted

Related Issues

• [Bug] Webchat: previous assistant message disappears when next message streams (blockStreamingDefault conflict) #33641 — assistant message disappears when next message streams in (closed, but different symptom)
• Control UI chat flickers sent user messages, they disappear briefly then reappear #66207 — messages flicker then reappear (closed)
• Control UI: Sent message briefly disappears then reappears (sometimes stays hidden) #67412 — messages briefly disappear then reappear (closed)
• Control UI: Messages disappear during tool execution #37083 — messages disappear during tool execution (closed)
• [Bug]: WebChat CLI runner — assistant replies invisible + user messages erased after each turn #68611 — CLI runner erases conversation history (closed)
• Streamed assistant messages not persisted in transcript (Control UI / webchat) #77324 — streamed assistant messages not persisted in transcript (open)

Environment

• OpenClaw: 2026.5.3-1 (2eae30e)
• OS: macOS 25.3.0 (arm64)
• Channel: webchat (openclaw-control-ui)
• Access: local via Kakarot Mini node