I installed a trial of Configuration Manager 2016 Technical Preview 4 and set up and configured the Software Update point. I wasn’t able to synchronize any updates.
I checked wsyncmgr.log and saw Sync failed: WSUS update source not found on site
The workaround was to configure the Software Update Point and disable/remove all Classifications and Products and then to schedule another sync.
After this, I scheduled another sync, and the sync completed.
I then went back and re-configued the Software Update Point for the Classifications and Products I wanted, then scheduled another sync and it worked fine.