Steps to reproduce
- Go to any Talk page, e.g. your user talk page.
- Write some text for a new topic, or a reply, but don't submit it yet.
- Take the device offline.
- Try submitting the message.
- A snackbar is shown with a meaningful error.
- The user is able to try re-submitting the message.
- A snackbar is shown saying "Unknown error occurred."
- The "Submit" button becomes disabled, and I'm no longer able to resubmit the message.