Plesk panel is slow: Error during WebSocket handshake

Symptoms

• Plesk panel is slow: Plesk menus take a considerable amount of time to load.

• Browser DevTools (F12) shows the following errors under Console tab:

  Failed to load resource: the server responded with a status of 404 (Not Found)
  :8443/manifest.webmanifest?1607564336:1 Manifest: Line: 1, column: 1, Syntax error.
  WebSocket connection to 'wss://example.com:8443/ws' failed: Error during WebSocket handshake: Unexpected response code: 502

Cause

PleskWebSocket service is down.

Resolution

1. Connect to the server via RDP.

2. Go to Windows Start > Services page and restart PleskWebSocket service by right-click on PleskWebSocket > Restart.

3. If the issue persists reinstall PleskWebSocket and restart the service using CMD commands below:

   plesk sbin nssmmng --reinstall-service --name=PleskWebSocket

   net start PleskWebSocket