Press on the torrent file that is at 0% to select it, then tap the Pause button. Press on the torrent again to select it, then tap the Resume button.  If this does not work, click on More Actions and select Resume All option.  

In addition, if you have an antivirus installed, this might be blocking the app's access to the internet. We recommend adding an exception or temporarily disabling it. You may also want to try turning off any VPN and Proxy connections you have in place.