Same here since some time ago.
No firewall, antivirus, router nor any other things in the middle, one day kad was working and after an apt update the kad network is firewalled.
Tried to downgrade amule to cvs versions where I know it was working but still firewalled!! weird, isn't?
Also tried to move some .dat files out of the amule dir, no luck, also I don't know even which files are related to kad. I'll try to reset all config to default.