Hello stokkie,
A unit can use a lot of bandwidth if it is trying to send a message to an IP address which it can not reach. To resolve this you need access to the unit.
Are you able to access the web interface of the QuadCore? If you can, access the web interface, please take a look at the destination IP of Art-Net. If the destination IP is not reachable at all times you may want to consider changing the destination IP to 255.255.255.255. This is called a broadcast address. Which will make the unit send Art-Net to your whole network. (Which is always reachable.) This option can also be changed in the vManager.
If you are unable to access the unit or this does not resolve your issue please contact us.
Best regards,
Guido