Wait... so you can confirm that you managed to import a Mycelium HD wallet into Electrum by clicking the Options button, ticking the "BIP39 Seed" option and then using the Mycelium seed words in Electrum?
Nobody tested it with multiple mycelium accounts, but this quote suggests it won't work with a second mycelium account.
Electrum only supports the first/default wallet/account of the in BIP32 described HD wallets.
See here: https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki
I have tested with a multiple mycelium account wallet.
It will work for other accounts; however, you have to restore them individually. Meaning, follow the process outlined prior for each account within the wallet seed. You get a popup asking which account you want to restore.
My seed has 6 accounts. 0-5 I restored the first 4 as tests to know that it works.