Welcome to the forum.
Can you give us a few more details to help us diagnose your issue please. What device are you using? R1 or XR500? what is your physical setup? wall > modem > Netduma > all devices or wall > modem/router combo > Netduma > all devices, or something different? Are you using a wired PC to test?
There are also helpful guides here:
Netduma R1 optimal settings: http://support.netduma.com/support/solutions/articles/16000023979-optimal-setti