Another possibility I can think of is that you used a fake wallet to send your transaction, so they modify the transaction output but show the wrong details to trick you. Did you verify the files before you installed the app? Have you tried to open your wallet on a new device that is free from malware etc as mentioned above? I'm sure your PC was compromised, no update made Bitcoin Core or Electrum spend that much to a change address, especially one that your wallet doesn't control. I'd try to reinstall/format before I use it again. CMIIW.