Computers not showing up in Desktop Central

After successfully installing DCAgent on a machine it is hit and miss whether or not it will show up in Desktop Central. Those that don't show up in DC do show up in ServiceDesk and have their hardware and software listed.

We deploy software regularly through DC so need to be able to select the PC but they are not available as an option. I had three systems last week not show up and this week another one is not showing up. Tried rebooting, tried rejoining the domain, tried uninstalling DCAgent using the batch uninstall and reinstalling.

please advise.
Thanks
Ryan