You may have to export and import the cert from your FMC in to the datasource configured on the ERC.
Apply changes and roll-out policies. If that doesn't work, deleting the old eStreamer client and making a new one, export cert, import cert, apply, and roll out policies; Should do the trick.
I have had several times of the above scenario present itself and the above were steps taken to get to a resolution.
Thanks
T.