OEM 12c Issue: Error "Failed to connect to target database. Regions that fetch real-time data from target database will not be displayed. Closed Connection" while connecting to RAC database through 12cR3 grid.

You may see this error "Failed to connect to target database. Regions that fetch real-time data from target database will not be displayed. Closed Connection" while navigating to a RAC database page in OEM 12cR3 grid.

This error is caused due to the Bug 17575631. 

You need to apply the patch for bug 17575631 to stop this error.