Wow, this thread got me worried, 'cause blockchain.com is what I use for my BTC... I have a 2FA plus store my password rather safely. I just checked my balance to see whether everything is intact, and luckily I was not robbed... I will also soon receive the new Ledger wallet I won in a competition. Perhaps I should move my funds to this offline wallet, after all.
Is there a particular reason why you are using blockchain dot com? I don't see it offer much utility at all. It requires you to pay much higher fees due to them not supporting Segwit, which also means that you can't send funds to a native bc1 Segwit address.
At the same time, though, just today I came by a thread about money disappearing from Ledger Nano S in a mysterious way. That makes me wonder now whether there's any safe way to store Bitcoins, really. The way that gives sole responsibility to the owner. Paper wallet, I guess? Good luck with the investigation of what happened to your money!
Money doesn't just disappear from a Ledger hardware wallet. The person either bought a Ledger from a malicious website that has it already set up for him, which means that the one who set it up also owns a copy of the seed, or the person stored his seed online and it got compromised one way or another.