i just need to migrate to recover some lost bitcoins as many addresses were generated and they don't apear on my electrum wallet.
i had same problem with mycelium android wallet and i migrated to multibit hd by using the mycelium seed and it worked ! but with electrum i'm still stuck.
Electrum seeds are only for use on Electrum AFAIK.
Electrum has a gap limit that pre-generates address till 20 unused addresses are found. I suspect that this would be the main problem you are facing. To generate more address from the seed, use
wallet.create_new_address()
in your console.