Have you checked the derivation path on the Iancoleman tool under "BIP32 Derivation Path" that's the correct derivation path that you need to use when importing the BIP39 seed into Electrum to get the correct legacy wallet.
BIP 32 defines the path to HD wallet, legacy address derivation path is different.
BIP 32: m/0'/0/0 for path to HD wallet
BIP 44: m/44'/0'/0'/0/0 for Legacy