Hi Luke,
some checks
- subzones where endpoint registers should be "treat as authenticated" or "check credentials"
- presence server and presence UA is truned ON
- presence uri is configured properly under TMS in provisioning config template.
- check if any transform or search rule unknowingly blocking the subscribe message to reach presence server.
if this doesn't help then i will suggest you to start the logs on VCS server and then register two endpoints and see what happens when the endpoints subscribe for presence.
Regards
Alok