Now I have the complete picture. Let me write the investigation report.
Issue #3433: Container error: Stack not ready after 5000ms. Reason: Timeout waiting for shape data to be loaded
The Electric container enters an unrecoverable error state after restart, emitting Stack not ready after 5000ms. Reason: Timeout waiting for shape data to be loaded. A simple docker compose restart doesn't fix it because persistent shape data survives the restart; only docker compose down && docker compose up (which removes volumes/data) resolves the issue. All API requests get 503 responses indefinitely.