Recently I had problem with my Ubuntu, Whenever I tried to open a website my Chromium told me that a Network Change has been detected and after 1-2 reload that sites would load and sometimes failed to load fully.
After looking up for that problem, I found out many other people had same problem and it has something to do with “avahi-daemon”.
According to the links I found in Ubuntu forums, this problem comes from IPv6 in Ubuntu and disabling that service will fix it, I tried it and it worked:
# create the long-life config file
echo "net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1" | sudo tee /etc/sysctl.d/99-my-disable-ipv6.conf
# ask the system to use it
sudo service procps reload
# check the result