flippener before this incoming transaction which is now gone your Electrum wallet is empty?I see you send all your BTC before and in that moment everything is normal-but after that did you upgrade your Electrum wallet because I see you are using latest 3.0.3 version?

I think you are download fake Electrum 3.0.3 version maybe and it is just waiting for any incoming transaction,it is happen to many others users because there is so many fake sites which pay to Google to place their ad on the top of search results.Check here : https://bitcointalk.org/index.php?topic=2660792.0

If this is not case then you exposed your private keys/seed somewhere where you did not to do that.Too bad that you did not change withdraw address on Poloniex to your primary wallet.