The problem is that volumio does not even start when the screen is connected.
If I connect the screen after startup, turn the touch plugin off and on again, I get this:
Nov 15 15:31:29 volumio volumio[1166]: info: Enabling plugin touch_display
Nov 15 15:31:29 volumio volumio[1166]: info: Loading plugin “touch_display”…
Nov 15 15:31:29 volumio volumio[1166]: info: Applying required configuration parameters for plugin touch_display
Nov 15 15:31:29 volumio volumio[1166]: info: PLUGIN START: touch_display
Nov 15 15:31:29 volumio volumio[1166]: info: Loading i18n strings for locale en
Nov 15 15:31:29 volumio sudo[3226]: volumio : TTY=unknown ; PWD=/ ; USER=root ; COMMAND=/bin/systemctl daemon-reload
Nov 15 15:31:29 volumio sudo[3226]: pam_unix(sudo:session): session opened for user root by (uid=0)
Nov 15 15:31:29 volumio systemd[1]: Reloading.
Nov 15 15:31:29 volumio systemd[1]: [/lib/systemd/system/mpd.service:18] Unknown lvalue ‘ProtectKernelTunables’ in section 'Service’
Nov 15 15:31:29 volumio systemd[1]: [/lib/systemd/system/mpd.service:19] Unknown lvalue ‘ProtectControlGroups’ in section 'Service’
Nov 15 15:31:29 volumio systemd[1]: [/lib/systemd/system/mpd.service:20] Unknown lvalue ‘ProtectKernelModules’ in section 'Service’
Nov 15 15:31:29 volumio systemd[1]: [/lib/systemd/system/mpd.service:23] Unknown lvalue ‘RestrictNamespaces’ in section 'Service’
Nov 15 15:31:29 volumio systemd[1]: Configuration file /lib/systemd/system/spop.service is marked executable. Please remove executable permission bits. Proceeding anyway.
Nov 15 15:31:29 volumio systemd[1]: Configuration file /lib/systemd/system/spop.service is marked world-writable. Please remove world writability permission bits. Proceeding anyway.
Nov 15 15:31:29 volumio sudo[3226]: pam_unix(sudo:session): session closed for user root
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: systemctl daemon-reload succeeded.
Nov 15 15:31:29 volumio sudo[3246]: volumio : TTY=unknown ; PWD=/ ; USER=root ; COMMAND=/bin/systemctl start volumio-kiosk.service
Nov 15 15:31:29 volumio sudo[3246]: pam_unix(sudo:session): session opened for user root by (uid=0)
Nov 15 15:31:29 volumio systemd[1]: Starting Volumio Kiosk…
Nov 15 15:31:29 volumio systemd[1]: Started Volumio Kiosk.
Nov 15 15:31:29 volumio startx[3251]: X.Org X Server 1.18.4
Nov 15 15:31:29 volumio startx[3251]: Release Date: 2016-07-19
Nov 15 15:31:29 volumio startx[3251]: X Protocol Version 11, Revision 0
Nov 15 15:31:29 volumio startx[3251]: Build Operating System: Linux 4.4.26-v7+ armv7l Raspbian
Nov 15 15:31:29 volumio startx[3251]: Current Operating System: Linux volumio 4.19.118-v7l+ #1311 SMP Mon Apr 27 14:26:42 BST 2020 armv7l
Nov 15 15:31:29 volumio startx[3251]: Kernel command line: coherent_pool=1M 8250.nr_uarts=0 cma=64M bcm2708_fb.fbwidth=640 bcm2708_fb.fbheight=480 bcm2708_fb.fbswap=1 smsc95xx.macaddr=DC:A6:32:5A:82:9A vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000 splash quiet plymouth.ignore-serial-consoles dwc_otg.fiq_enable=1 dwc_otg.fiq_fsm_enable=1 dwc_otg.fiq_fsm_mask=0xF dwc_otg.nak_holdoff=1 console=ttyS0,115200 kgdboc=ttyS0,115200 console=tty1 imgpart=/dev/mmcblk0p2 imgfile=/volumio_current.sqsh elevator=noop rootwait bootdelay=5 logo.nologo vt.global_cursor_default=0 loglevel=0 snd-bcm2835.enable_compat_alsa=1 snd_bcm2835.enable_headphones=1
Nov 15 15:31:29 volumio startx[3251]: Build Date: 11 November 2016 11:59:59AM
Nov 15 15:31:29 volumio startx[3251]: xorg-server 2:1.18.4-2+rpi1 (https://www.debian.org/support)
Nov 15 15:31:29 volumio startx[3251]: Current version of pixman: 0.32.6
Nov 15 15:31:29 volumio startx[3251]: Before reporting problems, check http://wiki.x.org
Nov 15 15:31:29 volumio startx[3251]: to make sure that you have the latest version.
Nov 15 15:31:29 volumio startx[3251]: Markers: (–) probed, (**) from config file, (==) default setting,
Nov 15 15:31:29 volumio startx[3251]: (++) from command line, (!!) notice, (II) informational,
Nov 15 15:31:29 volumio startx[3251]: (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
Nov 15 15:31:29 volumio startx[3251]: (==) Log file: “/var/log/Xorg.0.log”, Time: Sun Nov 15 15:31:29 2020
Nov 15 15:31:29 volumio startx[3251]: (==) Using config directory: “/etc/X11/xorg.conf.d”
Nov 15 15:31:29 volumio startx[3251]: (==) Using system config directory “/usr/share/X11/xorg.conf.d”
Nov 15 15:31:29 volumio startx[3251]: modprobe: FATAL: Module g2d_23 not found.
Nov 15 15:31:29 volumio sudo[3246]: pam_unix(sudo:session): session closed for user root
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: systemctl start volumio-kiosk.service succeeded.
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: Volumio Kiosk started
Nov 15 15:31:29 volumio volumio[1166]: info: CoreCommandRouter::executeOnPlugin: system , getConfigParam
Nov 15 15:31:29 volumio volumio[1166]: info: CoreCommandRouter::volumioGetState
Nov 15 15:31:29 volumio volumio[1166]: info: CorePlayQueue::getTrack 0
Nov 15 15:31:29 volumio volumio[1166]: info: Done.
Nov 15 15:31:29 volumio volumio[1166]: info: CoreCommandRouter::volumioGetState
Nov 15 15:31:29 volumio volumio[1166]: info: CorePlayQueue::getTrack 0
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: No Raspberry Pi Foundation touch screen detected.
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: Using /boot/config.txt instead of /boot/userconfig.txt.
Nov 15 15:31:29 volumio volumio[1166]: info: touch_display: Un-/commenting gpu_mem settings in /boot/config.txt.
Nov 15 15:31:30 volumio volumio[1166]: info: touch_display: Using Xserver unix domain socket /tmp/.X11-unix/X0
Nov 15 15:31:30 volumio sudo[3288]: volumio : TTY=unknown ; PWD=/ ; USER=root ; COMMAND=/bin/sed -i -e /Option “TransformationMatrix”/d /etc/X11/xorg.conf.d/95-touch_display-plugin.conf
Nov 15 15:31:30 volumio sudo[3288]: pam_unix(sudo:session): session opened for user root by (uid=0)
Nov 15 15:31:30 volumio sudo[3288]: pam_unix(sudo:session): session closed for user root
Nov 15 15:31:30 volumio volumio[1166]: info: touch_display: Touchscreen transformation matrix removed.
Nov 15 15:31:30 volumio volumio[1166]: info: touch_display: Setting screensaver timeout to 120 seconds.
Nov 15 15:31:31 volumio pulseaudio[3357]: Stale PID file, overwriting.
Nov 15 15:31:31 volumio pulseaudio[3357]: Unable to contact D-Bus: org.freedesktop.DBus.Error.Spawn.ExecFailed: /usr/bin/dbus-launch terminated abnormally without any error message
Nov 15 15:31:31 volumio pulseaudio[3357]: Unable to contact D-Bus: org.freedesktop.DBus.Error.Spawn.ExecFailed: /usr/bin/dbus-launch terminated abnormally without any error message
Nov 15 15:31:31 volumio bluetoothd[751]: Endpoint registered: sender=:1.37 path=/MediaEndpoint/A2DPSource
Nov 15 15:31:31 volumio bluetoothd[751]: Endpoint registered: sender=:1.37 path=/MediaEndpoint/A2DPSink
Nov 15 15:31:31 volumio pulseaudio[3357]: org.bluez.Manager.GetProperties() failed: org.freedesktop.DBus.Error.UnknownMethod: Method “GetProperties” with signature “” on interface “org.bluez.Manager” doesn’t exist