Blockchain.info's wallet can be extremely buggy and is poorly written. If you truly want your Bitcoin to be safe and to use a legitimate properly written wallet software, you should use a desktop wallet like Electrum or Bitcoin Core.

Your Bitcoin cannot simply disappear without there being a transaction sending it away from your wallet. If it is "disappearing" then there is probably an issue with your wallet software.

As for Bitcoin being sent to the wrong address, there are malware that will replace any address you copy with the address of an attacker so you end up sending Bitcoin to the wrong place. You should make sure that your computer does not have a virus.