Cause
The Shadow renderer has encountered a critical error while running Shadow.
Solution
If you've encountered error R: -1, restart the Shadow application, Shadow Box, or Shadow Ghost. This will usually solve the problem.
You can also try turning off Shadow.
To shut down Shadow on a device with a Windows, macOS, or Ubuntu operating system, click the Help 
icon → Shut down Shadow.
To shut down Shadow via a mobile application, such as iOS or Android, tap Settings → Turn off Shadow.
If the problem persists, contact Support and let our team investigate further.