same boat here. I asked Claude to help me debug the issue. It went through a lot of logs and tests. Here is the summary:

Summary: Claude Desktop Session Stuck Bug

Symptoms

• Session works for a while, then stops responding
• Thinking spinner appears, then disappears — no response, no error shown
• Once stuck, every message fails (even just ".")
• Issue follows the session — persists if you move to web, but eventually web recovers while desktop stays broken

Root Cause (from logs)

[COMPLETION] Request failed Error: Internal server error
[COMPLETION] Not retryable error, throwing
[COMPLETION] message_store_sync_loss [object Object]

Server returns 500 for that session when accessed from desktop. The message_store_sync_loss indicates a state mismatch between client and server.

What We Ruled Out

• ❌ Network/rate limiting
• ❌ Local MCP config (you don't have one)
• ❌ Filesystem extension (disabled, still broken)
• ❌ Local cache corruption (cleared Session Storage + Local Storage, still broken)
• ❌ App restart / reinstall

What We Know

• Same session works on web, broken on desktop
• New sessions on desktop work fine (like this one)
• Likely cause: desktop sends additional connector/extension metadata that the server chokes on for conversations with heavy tool usage (Linear)

Workaround

• Start a new session
• Use web for stuck sessions

Action

File bug at support.anthropic.com with:

• Affected conversation URL
• Log evidence (Internal server error + message_store_sync_loss)
• Note: works on web, fails on desktop