Hello Joseph,
as we have no experience using gsyncit, I am unable right now to tell you the cause of this.
As for the technical background on sync with GTasks, every time you start the sync between Astrid and GTasks, it only requests changes for the time since the last successful sync (to save network-traffic). So it seems, that GTasks doesnt report the new task from gsyncit/Exchange to Astrid because its timestamp might be wrong.
Please check your time-settings of your Exchange-server/gsyncit-server (or consult your admin) and check the timezone-setting of your GTasks-account and your Astrid-phone to be correct.
If its correct or doesnt help, you could also try logging out and back in to GTasks from within Astrid to see if this helps syncing in the new tasks from gsyncit.
The reason for this would be, that Astrid does a full sync of every task after a fresh login since it doesnt have a timestamp of the last successful sync anymore.
Hope this helps,