Are you performing the proper WSUS maintenance including but not limited to running the Server Cleanup Wizard (SCW), declining superseded updates, running the SQL Indexing script, etc.?
You'll also want to review:
1TB of updates is HUGE (normally, with WAM, the WsusContent store is <200GB and usually <100GB).
For your clients not reporting: you'll also want to review
Pay attention to the troubleshooting part below the Client Side Script.
Lastly, it may not be worth saving. You can re-install WSUS fairly easily and start new in just a few hours.