I've done multiple firmware updates without problem, but you are alays warned to make sure you have a backup of the mnemonic prior to upgrading. Are seeing the same wallet addresses on the new firmware ? If you have no passphrase you should see the same addresses, and if you have entered the same passphrase again you should see the same HD tree. Do you have any old transactions in from phone wallet to Trezor accounts you can check ?

Edit : Must have been I page back or something....