By default SyncBack will disconnect from a UNC path once the profile has finished. If, however, you have set it not to disconnect then it may be using all available network connections. To force it to disconnect at the end of a run: modify your profile, enable Expert mode, and go to the Network -> Advanced page of the profile configuration. Untick the option(s) Do not disconnect from the network after the profile has run.
Bear in mind this will only affect behavior on future runs. You may need to take remedial action (maybe reboot) to clear existing connections.