Check the NAT type that registers in-game. Is it Open, Moderate or Strict? Also, what do you have your search preferences set to (Best, Normal or Any)?
You may want to try the following:
- Reboot your router.
- Try using a wired connection in order to sustain the connection quality.
- To help identify if there is an issue with the router or blocked ports, try connecting directly through the modem.
- Establish a static IP address and port forward.
Although you did not specify the platform you are on, here are the port numbers you will need in order to port forward:
Xbox: Activision Support
Should you have any questions on how to port forward, please contact your ISP or the router manufacturer.