The issue happens because the server fails to send APNs notification.

To resolve the issue, do the following:

1. Make sure the Local Communication Server (LCS) has been upgraded to the same version as Management Server. It can be checked using the dashboard or EXE files (e.g. ccs.exe and ManagementServer.exe).
2. Check that you can successfully save the Communication Server settings.
3. Restart the LCS service to check the issue.
4. Ensure that the port 2195 is enabled in firewall. Communication Server uses this port to communicate with Apple Push Notification Services.

After resolving the issue, you may also notice the following entry in the masterserver.log:

017-05-22 11:00:02 MasterServer ERROR [0x00000c48]  [source\tm_proxy_setting.cpp(41)]- tmms_master::GetProxySetting  ->Failed to get proxy info from db

The log above always contains some errors, but there is no need to worry about. It is simply the log level set in the code.