@MG18: I don't see that the KEEPALIVE param was available in SAS 9.3. Perhaps another contributor can comment or you can also open a track with SAS Tech Support.
My suspicion remains the firewall. In my experience, the network security teams will make updates to firewall parameters from time to time without informing the user communities. I suggest you ask your firewall team if they have modified the idle timeout or any other settings that would apply to your communications. Often times these are global settings for the entire firewall policy and not specific to your set of rules.