Occasionally you may see a network warning in the bottom right corner of the screen.
This can occur for two reasons.
The most common reason is that your device has lost internet connectivity. Check your wifi connection and make sure your device is online. Try refreshing the page.
If the warning persists, the blockchain network might be experiencing downtime. This is an extremely rare incident for most networks. In this event, the only option is to wait for the blockchain developers (e.g. Ethereum, Polygon, Arbitrum, or Optimism) to resolve the issue.