Freezes and wifi dropouts
Ubuntu has always has issues holding wifi stable in my experience but upgrading to Cosmic from Bionic on a Dell XPS13, bought with Ubuntu installed, which has been perfect (bar the occasional wifi dropout) since November now has random freezes (fixed only by holding power down to reboot) and very frequent wifi disconnects which aren't always recovered by restarting network-manager. Had to setup my VPNs again too as existing ones failed to start after updating to Cosmic.
Worst update in a while for me.
Oh and my workspace switching shortcuts all got reset along with the workspace layouts. Grrrrr