If I understand correctly, one in 5-6 calls results in "Video stream failed to connect error". This is most likely a firewall or router configuration issue.
If you are video chatting with different people and you are sometimes getting a "video stream failed to connect error", the person you are chatting with probably has a firewall or configuration issue.
If you are testing with yourself and sometimes getting that error, you might have firewall or configuration issues.
To verify that you firewall is configured correctly, try running this diagnostic tool.
If you would like to see when your users are experiencing this error and would like to educate them on the diagnostic tool or what the possible causes are, you can listen to exception events (#1013 in your case)
Disclaimer: I work at TokBox.
Good Luck!