I'm trying Electrum now so I decided to sweep 18sDqHgssw8MQKpjvUyKPxUPXdP7p9ZuSJ to see how it goes. Entered private key on wallet > Private keys > Sweep but the address in the sweeping screen ( 181GfHAqsGG4QttbGvHCNsv1hXVBAv54fJ ) isn't receiving the bitcoin. Although I'm' receiving a transaction ID: a6b9601d12c15a823494662128b8c4aa97cac436465a044d3031845df8dd8547 , blockchain.info shows the message: Sorry we could not find any blocks or transactions matching this hash when I look for it
Sweeping is not sending funds to an address, but sends all currently available funds on that address towards another one in that wallet.
As there have never been any funds on the given address the TX was probably never broadcasted or if it was broadcasted did not make it very far.