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.

Also, in derived addresses on the left side, it should show the path of your BTC address and what derivation path your BTC address belongs. Look at the image below as a reference



Or alternatively, export the private key since you said you get the correct wallet using iancoleman then export the private key from that tool and import it to Electrum. Make sure that you use this tool on an offline PC or else it's not safe anymore to reuse that wallet.