Note that the checksum in BIP39 seeds is weak. A 12 word BIP39 seed only has a 4 bit checksum. There is a 1/16 chance that a random selection of 12 words from the wordlist is a valid seed.
Please also note, the crux of the issue lies in this alleviation/mitigation.
That chaotic combination of mnemonic phrases is a BIP-39 seed, but it cannot be imported into other mainstream wallets like Trust Wallet, Phantom, or MetaMask, even though these wallets do support BIP-39 seed phrases!!"
"That chaotic combination of mnemonic phrases can only be successfully imported into Electrum wallet using the [BIP-39] format option, which is the strangest part."
"All I've said so far is to express my suspicion that Electrum might have some unknown mechanism that causes this result