After an update I made a week ago, I noticed that my Wifi connection has gotten a lot worse, it keeps disconnecting every now and then.
The weird thing is, I can almost replicate its disconnection simply by opening a terminal and using the sudo pacman -Syyu command
You need to post more details by using command line : inxi -n or ip link ( from your terminal or tty) . I will suggest that you change mirrors (repositories of Manjaro) for your fastest access to local position and update with: sudo pacman-mirrors --fasttrack 10 && sudo pacman -Syyu
I hope this could be some help