The correctness of the 24 mnemonic recovery words is verified by the embedded checksum which is part of the last recovery word.

If you have an additional mnemonic passphrase then you have to be very careful to type it correctly, because there's no right or wrong. Any unique mnemonic passphrase will yield an unique wallet with different addresses. The smallest error gives you an empty wallet.

It's hard to say what you're doing wrong. Can we rule out issues with the Electrum server connection?
Can we rule out a wrong derivation path? Potential issues with gap limit?