This is a common issue on Wireshark under Linux due to permission issue. You may also get the following error while trying to do a Capture.
You didn’t specify an interface on which to capture packets.
This can be fixed by the following commands.
sudo dpkg-reconfigure wireshark-common sudo usermod -a -G wireshark $USER
Then Reboot or logout and log back it via the following command.
gnome-session-quit --logout --no-prompt