If your VPNinja account is constantly disconnecting and restarting - it's probably caused by two connections on the same client technology (OpenVPNinja or PPTP) trying to connect to the same server at the same time.
While VPNinja allows one account to connect two simultaneous devices at the same time, those two connections cannot be made on the same server on the same technology simultaneously.
Make sure you are not connecting to the same server on the same client technology. If you are sharing your VPNinja with a friend, be sure you are using different servers if you both decide to use OpenVPNinja. Or, if you both want to connect to the same server, make sure one of you is using PPTP, and the other OpenVPN.