QBittorrent is based on the Qt toolkit and libtorrent-rasterbar library. Help qBittorrent. QBittorrent is developed by volunteers in their spare time. If you like this piece of software, please make a donation and help it survive. Donation info here. If you want to help in translating qBittorrent, see these instructions. QBittorrent Features.
This happened to me too.
Ubuntu 16.04 LTS
qBittorrent 4.0.3 (64-bit)
QT: 5.5.1
Libtorrent: 1.1.5.0
Boost 1.58.0
I have tried removing the ~/.config/qBittorrent/ folder but it still doesn't work.
Here is the log (which I think it doesn't show anything interesting):
Qbittorrent Not Downloading At Full Speed
(N) 2017-12-30T13:27:13 - qBittorrent v4.0.3 iniciado
(I) 2017-12-30T13:27:16 - qBittorrent está tratando de escuchar en cualquier interfaz, puerto: 8999
(N) 2017-12-30T13:27:16 - Peer ID: -qB4030-
(N) 2017-12-30T13:27:16 - HTTP User-Agent is 'qBittorrent/4.0.3'
(I) 2017-12-30T13:27:16 - DHT [Activado]
(I) 2017-12-30T13:27:16 - Buscar pares locales [Activado]
(I) 2017-12-30T13:27:16 - PeX support [Activado]
(I) 2017-12-30T13:27:16 - Modo Anónimo [Desactivado]
(I) 2017-12-30T13:27:16 - Cifrado [Activado]
(I) 2017-12-30T13:27:16 - Tracker integrado [Desactivado]
(I) 2017-12-30T13:27:16 - Soporte UPnP / NAT-PMP [Activado]
(I) 2017-12-30T13:27:16 - Base de datos GeoIP cargada. Tipo: GeoLite2-Country. Creada el: mié. dic. 6 20:48:19 2017.
(N) 2017-12-30T13:27:16 - Opciones guardadas correctamente.
(I) 2017-12-30T13:27:16 - qBittorrent está escuchando en la interfaz :: puerto: TCP/8999
(I) 2017-12-30T13:27:16 - qBittorrent está escuchando en la interfaz 0.0.0.0 puerto: TCP/8999
(I) 2017-12-30T13:27:16 - qBittorrent está escuchando en la interfaz 0.0.0.0 puerto: UDP/8999
(I) 2017-12-30T13:27:16 - IP Externa: 92.XXX.XX.XXX
(I) 2017-12-30T13:27:16 - UPnP/NAT-PMP: Puerto mapeado correctamente, mensaje: successfully mapped port using UPnP. external port: TCP/8999
(I) 2017-12-30T13:27:16 - UPnP/NAT-PMP: Puerto mapeado correctamente, mensaje: successfully mapped port using UPnP. external port: UDP/8999
(N) 2017-12-30T13:27:55 - 'LibreOffice_5.4.4_Linux_x86-64_deb.tar.gz' agregado a la lista de descargas.
(I) 2017-12-30T13:28:13 - Soporte UPnP / NAT-PMP [Desactivado]