Can you provide more information here? If you test the log source, does any data return? If you disable/re-enable, does the log source collect data? Also, is this for all event log types, Security, Application, and System or just one type of data?
I'm not sure if you've opened a case on this issue, but this sounds like something that we want to confirm in a support case. If your log source is configured with the Microsoft Windows Event Log over MSRPC protocol, then we are investigating issues with 'binding' errors that can cause the log source to unexpected stop and you should log your issue.
If you can provide more information, we can give more guidance, but without an error or more details on the log source configuration it makes it hard to troubleshoot in the forums.