gnome – Unable to use keyboard shortcut combination including Alt+Shift

Any shortcut combination involving Alt+Shift is not picked up. When I try to set (or use) shortcuts in PhpStorm that involve Alt+Shift nothing happens. I thought to start with it only affects PhpStorm but when I try to set those shortcuts in my terminal the keys are not working either. I already tried remove all Alt+Shift shortcut combinations from the system shortcuts that I could find but that didn’t help either.

These are all the shortcuts using either Alt or Shift:

$ gsettings list-recursively | grep '<Alt>'
org.gnome.desktop.wm.keybindings switch-group ('<Super>Above_Tab', '<Alt>Above_Tab')
org.gnome.desktop.wm.keybindings toggle-maximized ('<Alt>F10')
org.gnome.desktop.wm.keybindings cycle-windows ('<Alt>Escape')
org.gnome.desktop.wm.keybindings activate-window-menu ('<Alt>space')
org.gnome.desktop.wm.keybindings panel-main-menu ('<Alt>F1')
org.gnome.desktop.wm.keybindings close ('<Alt>F4')
org.gnome.desktop.wm.keybindings switch-windows ('<Alt>Tab')
org.gnome.desktop.wm.keybindings panel-run-dialog ('<Alt>F2')
org.gnome.desktop.wm.keybindings unmaximize ('<Super>Down', '<Alt>F5')
org.gnome.desktop.wm.keybindings show-desktop ('<Primary><Super>d', '<Primary><Alt>d', '<Super>d')
org.gnome.desktop.wm.keybindings cycle-group ('<Alt>F6')
org.gnome.mutter.wayland.keybindings switch-to-session-4 ('<Primary><Alt>F4')
org.gnome.mutter.wayland.keybindings switch-to-session-10 ('<Primary><Alt>F10')
org.gnome.mutter.wayland.keybindings switch-to-session-3 ('<Primary><Alt>F3')
org.gnome.mutter.wayland.keybindings switch-to-session-9 ('<Primary><Alt>F9')
org.gnome.mutter.wayland.keybindings switch-to-session-2 ('<Primary><Alt>F2')
org.gnome.mutter.wayland.keybindings switch-to-session-8 ('<Primary><Alt>F8')
org.gnome.mutter.wayland.keybindings switch-to-session-1 ('<Primary><Alt>F1')
org.gnome.mutter.wayland.keybindings switch-to-session-7 ('<Primary><Alt>F7')
org.gnome.mutter.wayland.keybindings switch-to-session-12 ('<Primary><Alt>F12')
org.gnome.mutter.wayland.keybindings switch-to-session-6 ('<Primary><Alt>F6')
org.gnome.mutter.wayland.keybindings switch-to-session-11 ('<Primary><Alt>F11')
org.gnome.mutter.wayland.keybindings switch-to-session-5 ('<Primary><Alt>F5')
org.gnome.settings-daemon.plugins.media-keys magnifier-zoom-in ('<Alt><Super>equal')
org.gnome.settings-daemon.plugins.media-keys volume-mute-quiet-static ('<Alt>XF86AudioMute')
org.gnome.settings-daemon.plugins.media-keys magnifier-zoom-out ('<Alt><Super>minus')
org.gnome.settings-daemon.plugins.media-keys volume-down-quiet-static ('<Alt>XF86AudioLowerVolume')
org.gnome.settings-daemon.plugins.media-keys window-screenshot ('<Alt>Print')
org.gnome.settings-daemon.plugins.media-keys terminal ('<Primary><Alt>t')
org.gnome.settings-daemon.plugins.media-keys volume-up-quiet-static ('<Alt>XF86AudioRaiseVolume')
org.gnome.settings-daemon.plugins.media-keys screenreader ('<Alt><Super>s')
org.gnome.settings-daemon.plugins.media-keys magnifier ('<Alt><Super>8')
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-2 '<Alt>2'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-3 '<Alt>3'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-4 '<Alt>4'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-5 '<Alt>5'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-6 '<Alt>6'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-7 '<Alt>7'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-8 '<Alt>8'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-9 '<Alt>9'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-10 '<Alt>0'
org.gnome.Terminal.Legacy.Keybindings switch-to-tab-1 '<Alt>1'
$ gsettings list-recursively | grep '<Shift>'
org.gnome.desktop.wm.keybindings move-to-monitor-right ('<Super><Shift>Right')
org.gnome.desktop.wm.keybindings move-to-workspace-1 ('<Super><Shift>Home')
org.gnome.desktop.wm.keybindings move-to-monitor-left ('<Super><Shift>Left')
org.gnome.desktop.wm.keybindings switch-applications-backward ('<Shift><Super>Tab')
org.gnome.desktop.wm.keybindings switch-input-source-backward ('<Shift><Super>space', '<Shift>XF86Keyboard')
org.gnome.desktop.wm.keybindings move-to-monitor-down ('<Super><Shift>Down')
org.gnome.desktop.wm.keybindings move-to-workspace-last ('<Super><Shift>End')
org.gnome.desktop.wm.keybindings switch-group-backward ('<Shift><Super>Above_Tab')
org.gnome.settings-daemon.plugins.media-keys area-screenshot ('<Shift>Print')
org.gnome.settings-daemon.plugins.media-keys volume-up-precise-static ('<Shift>XF86AudioRaiseVolume')
org.gnome.settings-daemon.plugins.media-keys volume-down-precise-static ('<Shift>XF86AudioLowerVolume')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-1 ('<Shift><Super>1')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-2 ('<Shift><Super>2')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-3 ('<Shift><Super>3')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-4 ('<Shift><Super>4')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-5 ('<Shift><Super>5')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-6 ('<Shift><Super>6')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-7 ('<Shift><Super>7')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-8 ('<Shift><Super>8')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-9 ('<Shift><Super>9')
org.gnome.shell.extensions.dash-to-dock app-shift-hotkey-10 ('<Shift><Super>0')
org.gnome.Terminal.Legacy.Keybindings close-window '<Ctrl><Shift>q'
org.gnome.Terminal.Legacy.Keybindings find-previous '<Control><Shift>H'
org.gnome.Terminal.Legacy.Keybindings new-tab '<Ctrl><Shift>t'
org.gnome.Terminal.Legacy.Keybindings close-tab '<Ctrl><Shift>w'
org.gnome.Terminal.Legacy.Keybindings find '<Control><Shift>F'
org.gnome.Terminal.Legacy.Keybindings find-next '<Control><Shift>G'
org.gnome.Terminal.Legacy.Keybindings move-tab-right '<Ctrl><Shift>Page_Down'
org.gnome.Terminal.Legacy.Keybindings move-tab-left '<Ctrl><Shift>Page_Up'
org.gnome.Terminal.Legacy.Keybindings new-window '<Ctrl><Shift>n'
org.gnome.Terminal.Legacy.Keybindings paste '<Ctrl><Shift>v'
org.gnome.Terminal.Legacy.Keybindings copy '<Ctrl><Shift>c'
org.gnome.Terminal.Legacy.Keybindings find-clear '<Control><Shift>J'

So it seems to me that no system shortcuts could block the combination and I tried to figure out which program is catching the combination based on this answer:

$ KEY=shift+alt
$ xdotool keydown ${KEY}; xdotool key XF86LogGrabInfo; xdotool keyup ${KEY}

Gives me

/usr/lib/gdm3/gdm-x-session(2600): (II) Printing all currently active device grabs:
/usr/lib/gdm3/gdm-x-session(2600): (II) End list of active device grabs
/usr/lib/gdm3/gdm-x-session(2600): Printing all currently registered grabs
/usr/lib/gdm3/gdm-x-session(2600):   Printing all registered grabs of client pid 2504 /usr/bin/pulseaudio --daemonize=no --log-target=journal
/usr/lib/gdm3/gdm-x-session(2600):   Printing all registered grabs of client pid 2810 /usr/bin/gnome-shell
/usr/lib/gdm3/gdm-x-session(2600):   grab 0x40409425 (xi2), type 'ButtonPress' on window 0x3603505
/usr/lib/gdm3/gdm-x-session(2600):     detail 3 (mask 0), modifiersDetail 78 (mask 0)
/usr/lib/gdm3/gdm-x-session(2600):     device 'Virtual core pointer' (2), modifierDevice 'Virtual core keyboard' (3)
/usr/lib/gdm3/gdm-x-session(2600):       xi2 event mask 0x70 0 0 0
/usr/lib/gdm3/gdm-x-session(2600):     owner-events false, kb 1 ptr 1, confine 0x0, cursor 0x0
(...)
/usr/lib/gdm3/gdm-x-session(2600): End list of registered passive grabs

At (...) it first continues a long list of gabs like the one you can see and then simply list “Printing all registered grabs…” of other programs running but they to not have any grabs. What I am wondering is why it shows only passive grabs and not a single active grab… I tried that with different Alt+Shift combinations like Ctrl+Alt+Shift+N with the same result.

How can I figure out what blocks Alt+Shift combinations?