Slow WiFi since updating to 18.04
Solution 1:
I just fixed this on ubuntu 18.04 - turns out there is some kind of issue with 802.11n and iwlwifi Intel chips. The solution is to turn it off.
Check if it works first with:
sudo modprobe -r iwlwifi
sudo modprobe iwlwifi 11n_disable=1
Make it permanent with this command:
echo "options iwlwifi 11n_disable=1" | sudo tee /etc/modprobe.d/iwlwifi.conf
I did this and my wifi speeds instantly went back to normal.