The Locktime (`nLockTime`) value is [deliberately randomized][1] 
 back in order to discourage a subtle attack known as "Fee sniping".

You can read more about it [here in the PR](https://github.com/spesmilo/electrum/pull/4967).


  [1]: https://github.com/spesmilo/electrum/blob/a50f935aecc1a47dffce195808ed3b1839c8e3a0/electrum/wallet.py#L175