This error occurs when HomeKit is syncing things up with iCloud. The iOS device isn't able to get the home information synced from the iCloud account. Typically the issue resolves itself after several hours. Please wait a few hours and then try again. To resolve it, follow these steps, as outlined by Apple:
- Check your Internet and Wi-Fi connections.
- Update your iOS device to the latest version of iOS.
- Restart your iOS device.
- Verify Keychain is enabled in Settings > iCloud > Keychain.
- Verify Home is enabled in Settings > iCloud > Home.
- If you still have issues, turn off iCloud Keychain, then turn it back on. Make sure that you signed in to iCloud successfully.
- Sign out of your iCloud account and sign back in.
- If your iOS device is running iOS 10 and you have an Apple TV (4th Generation) or iPad setup as a Home Hub, please verify 2-factor authentication is enabled for the iCloud Apple ID.
- If the previous troubleshooting steps don't resolve the issue, we recommend going into the Apple Home App. You should see “Loading Accessories and Scenes”. After about 30 minutes the Apple Home app should pop up a message that says “This is taking awhile. Would you like to reset?" Continuing will reset the home information and allow you to set up your device.