@Rex,

 Found it's hanging in 'Ensure prerequisites for "gnome-calculator" are available'. And in #14 there are error about the gnome-calculator, so it should be related to this issue. Thanks!

$ snap change 1
Status  Spawn                     Ready                     Summary
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:39 EDT  Ensure prerequisites for "core" are available
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:39 EDT  Prepare snap "/var/lib/snapd/seed/snaps/core_6818.snap" (6818)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:39 EDT  Mount snap "core" (6818)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:39 EDT  Copy snap "core" data
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "core" (6818) security profiles
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Make snap "core" (6818) available to the system
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Automatically connect eligible plugs and slots of snap "core"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Set automatic aliases for snap "core"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "core" aliases
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run install hook of "core" snap if present
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Start snap "core" (6818) services
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run configure hook of "core" snap if present
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Ensure prerequisites for "gnome-3-26-1604" are available
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Prepare snap "/var/lib/snapd/seed/snaps/gnome-3-26-1604_82.snap" (82)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Mount snap "gnome-3-26-1604" (82)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Copy snap "gnome-3-26-1604" data
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "gnome-3-26-1604" (82) security profiles
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Make snap "gnome-3-26-1604" (82) available to the system
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Automatically connect eligible plugs and slots of snap "gnome-3-26-1604"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Set automatic aliases for snap "gnome-3-26-1604"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "gnome-3-26-1604" aliases
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run install hook of "gnome-3-26-1604" snap if present
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Start snap "gnome-3-26-1604" (82) services
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run configure hook of "gnome-3-26-1604" snap if present
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Ensure prerequisites for "gtk-common-themes" are available
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Prepare snap "/var/lib/snapd/seed/snaps/gtk-common-themes_1198.snap" (1198)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Mount snap "gtk-common-themes" (1198)
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Copy snap "gtk-common-themes" data
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "gtk-common-themes" (1198) security profiles
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Make snap "gtk-common-themes" (1198) available to the system
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Automatically connect eligible plugs and slots of snap "gtk-common-themes"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Set automatic aliases for snap "gtk-common-themes"
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Setup snap "gtk-common-themes" aliases
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run install hook of "gtk-common-themes" snap if present
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Start snap "gtk-common-themes" (1198) services
Done    6 days ago, at 03:39 EDT  6 days ago, at 03:40 EDT  Run configure hook of "gtk-common-themes" snap if present
Doing   6 days ago, at 03:39 EDT  -                         Ensure prerequisites for "gnome-calculator" are available
Do      6 days ago, at 03:39 EDT  -                         Prepare snap "/var/lib/snapd/seed/snaps/gnome-calculator_406.snap" (406)
Do      6 days ago, at 03:39 EDT  -                         Mount snap "gnome-calculator" (406)
Do      6 days ago, at 03:39 EDT  -                         Copy snap "gnome-calculator" data