Open System Preferences > Network and make sure only one network interface is enabled, preferably the one that was enabled when you initially installed Smoke.
Then select the network interface in the left-hand pane and click Advanced in the right-hand pane.
Make sure Configure IPv6 is set to “Link-local only” in the TCP/IP tab.
Also, if you have installed Parallels Desktop, VMWare, Oracle VirtualBox or any other application that creates virtual network interfaces, try to temporarily disable those interfaces to see whether export starts working.
Restart your Mac if you made any change to the network settings, then delete all stalled Backburner jobs and attempt to export again.