Can you see all your transaction History in Electrum tho? is the balance correct?
In Electrum... on the "Addresses" tab (Wallet -> Addresses), have you expanded both the "Change" section and the "Used" sections? (click the '>' symbol so it becomes a 'V' symbol)...
In Mycelium, are your addresses all in the same "account"? or are they in different "accounts"??:
Do you get Account 1 and Account 2 etc? or only 1 HD account? If they're in different accounts, to see them all in Electrum, you need to create a different wallet for each account... when you import the BIP39 seed and it asks for an account number, 0 = MyceliumAccount1, 1 = MyceliumAccount2 etc etc
The only other reason I can think of that they don't show... would be the gap limit issue