It's difficult for me to resolve something without the problem itself on my system :/.
So, i took the docker image which have the issues and i did what lpa did meaning :
% sudo pacman-key --lsign-key 1E389882EFEABB1AE7723A014B9100E679075EDF
% sudo pacman-key --keyserver 'hkps://keyserver.ubuntu.com' --refresh-keys 1E389882EFEABB1AE7723A014B9100E679075EDF
% sudo pacman-key --populate obarun
And the problem was gone.
Note: i'm currently pushing new version of obarun, pkgbuild and our docker images.
The hard solution can be
% sudo rm -rf /etc/pacman.d/gnupg
% sudo mkdir /etc/pacman.d/gnupg
% sudo pacman-key --init
% sudo pacman-key --populate obarun archlinux
But you will lost any keys that you imported manually. So, making a backup of your gnupg directory could be a good idea.