I have another problem.
I set the mirror server to United States
I close and reopen the settings window and I see that the mirror server has changed to Worldwide. (??)
Please post you own problems in you own topic, 1 problem pro topic. Post split, free of charge this time.
How about setting the mirror pool with the terminal then?
https://wiki.manjaro.org/index.php/Pacman-mirrors#Mirrors_for_your_country_only
The pamacGUI is known to have issues. It is better to use the command line. 
sudo pacman-mirrors -c United_States && sudo pacman -Syu
I believe this is a bug in the Add / Remove Applications (Pamac) software.
It is expected that pamac executes pacman-mirrors -c <country> - obviously it does not.
When this happens you need to use the terminal command.
First get a list of supported countries (the reason being that double word countres (for cli reasons) are spelled using a _ (lodash) instead of space)
pacman-mirrors --list
Then build a mirror pool for the country e.g. United_States
sudo pacman-mirrors --country United_States
Or maybe it attempts to do it but does not elevate its privileges through polkit first. 
Don’t know what track OP is, but on my unstable seems to be working.