[BUG] OAuth credentials not saved after successful connection via mcp.pipedream.com (since June 27th)

To Reproduce
1. Go to https://mcp.pipedream.com/
2. Select any app (e.g., Zoom, ActiveCampaign)
3. Click “Connect Account” and complete the OAuth flow
4. The message “Account connected successfully!” appears
5. Refresh the page
6. The app shows “Connect Account” again
7. In n8n, MCP Client returns:
Could not connect to your MCP server

Expected behavior

The connected account should remain saved and available after refreshing the page, and the MCP Client (e.g., n8n) should be able to retrieve and use the stored credentials as it did previously.

Additional context

This setup was working perfectly until June 27th, 2025. I had multiple apps connected and running correctly with the MCP Client in n8n and through AI agents. After that date, none of the connected credentials are saved or accessible, regardless of reconnection or new app_slug.

I have also tested rotating the slug, deploying a self-hosted MCP server, and using different browsers and sessions. The problem persists across all setups.

This issue is critical as it has halted all workflows relying on MCP-based authentication.