Wallet has the same Seed phrase but cannot be accessed without the private key

I have a wallet that has the same recovery phrase as all my other accounts but can never be imported into ANY wallet without a private key. I have checked the seedphrase and it matches exactly.

To confirm, I checked the mnemonic generator to check whether this account shows up on the list. It never did at all! I don't understand how an account like this can have the same recovery phrase but never show up at all. Why do I only have to use my private key to access this wallet? Is it because I imported it with a private key at the start? Am I forced to use my private key to import this wallet forever or is there any solution?