i'm having similar issue with deriving the private keys from the seed provided by Blockchain.info web wallet; Iancoleman tool gave me all the privkeys except for the address that held my bitcoin in time of hard-forks. I already contacted the the support team of blockchain.info but no answer
Two things that might be worth checking:1. If you imported a private key into your blockchain.info wallet, and your funds were on that private key/address, you won't be able to get the private key using the Mnemonic Code Converter (aka "Ian Coleman tool") and your b.info seed mnemonic. You should however be able to export it manually from within b.info wallet. (Settings -> Addressed -> Imported Bitcoin Addresses)
2. It has been a while, so I don't remember if b.info uses "change" addresses or not. I think they do. So, you may need to change the derivation path slightly to find the address that has your coins...
On the Mnemonic Code Converter, enter your seed mnemonic in the "BIP39 Mnemonic" box and then click the "BIP44" tab. You should see your "receive" addresses and private keys displayed at the bottom... now change the "External/Internal" value from 0 to 1. Now you should see your "change" addresses and associated private keys displayed a the bottom.
Hopefully, your "missing" address is here!
