When you have a sending wallet, we encrypt it to send to your other devices (without us being able to read it). We store the encryption key in your browser. If your browser’s storage got deleted, this key gets deleted and you’ll need to reenter the passphrase for it.

If you did not write down the key, you’ll need to reset your wallets and input your sending wallet details again.

@ek did I get that right? I think what happened here is they never sync’d their devices yet their automatically configured key was purged and now they are locked out.