downgrading to gjs-1.50.4 works around the issue. see https://www.reddit.com/r/archlinux/comments/7iadeq/dragging_icon_from_dock_on_gnome_freezes_mouse/
This bug documents a similar issue as well as this one. https://gitlab.gnome.org/GNOME/gjs/issues/21
Is this an issue with gjs-1.54.3 and gnome-shell-3.30.2? Latter also carries patch for https://gitlab.gnome.org/GNOME/gnome-shell/issues/1015
gnome-shell-3.30.2 with gjs-54.3 fixes the issue. This bug should be changed to reference gnome-shell-3.28
3.28 won't be fixed nor stabled; use 3.30 then.