All mobile wallets you mentioned are created as hot wallets, so they are trying to connect to the internet every time you open the app.
I suspect this is the main reason why you are having this error issues, since you disabled internet connection.
Airgap.it created app with special purpose to be used as cold wallet, but you can also generate seed phrases offline separately using iancoleman website:
https://iancoleman.io/bip39/