So I've managed to resolve this - basically I recreated the vpn server via the wizard having completely deleted the old server. ( I also deleted and recreated all certificates but I'm not sure if this was actually required).
Once I did that then the client export was showing the server in the drop-down list.
I tried many many different things to get my openvpn server working after the upgrade and I ran into this as a secondary issue when rebuilding it.
I have a feeling that this was actually because the recreated server was in peer-peer mode when I created it via the Add button and not the wizard - I didnt notice, and so the server would have been the wrong type for clients / exports.