After few suspends or detach-/attachments of USB devices libinput starts ignoring new devices due to too many input devices. Unnecessary to say there is only one device attached.
journalctr reports this behavior:
/usr/lib/gdm3/gdm-x-session[1407]: (**) PixArt USB Optical Mouse: always reports core events#
/usr/lib/gdm3/gdm-x-session[1407]: (**) Option "Device" "/dev/input/event295"
/usr/lib/gdm3/gdm-x-session[1407]: (**) Option "_source" "server/udev"
/usr/lib/gdm3/gdm-x-session[1407]: (II) event295 - PixArt USB Optical Mouse: is tagged by udev as: Mouse
/usr/lib/gdm3/gdm-x-session[1407]: (II) event295 - PixArt USB Optical Mouse: device set to 1000 DPI
/usr/lib/gdm3/gdm-x-session[1407]: (II) event295 - PixArt USB Optical Mouse: device is a pointer
/usr/lib/gdm3/gdm-x-session[1407]: (II) event295 - PixArt USB Optical Mouse: device removed
/usr/lib/gdm3/gdm-x-session[1407]: (EE) Too many input devices. Ignoring PixArt USB Optical Mouse
/usr/lib/gdm3/gdm-x-session[1407]: (II) UnloadModule: "libinput"
The bug seems related to a known libinput bug 1579567.
https://bugzilla.redhat.com/show_bug.cgi?id=1579567
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: xserver-xorg-input-libinput 0.27.1-1
ProcVersionSignature: Ubuntu 4.15.0-34.37-generic 4.15.18
Uname: Linux 4.15.0-34-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
BootLog: Error: [Errno 13] Keine Berechtigung: '/var/log/boot.log'
CurrentDesktop: ubuntu:GNOME
Date: Tue Sep 25 09:11:31 2018
DistUpgraded: Fresh install
DistroCodename: bionic
DistroVariant: ubuntu
MachineType: ASUSTeK COMPUTER INC. UX51VZA
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=de_DE.UTF-8
SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-34-generic root=UUID=05aab5a7-bef4-4178-acea-7bebfacf8766 ro quiet splash vt.handoff=1
SourcePackage: xserver-xorg-input-libinput
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/03/2012
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: UX51VZA.204
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UX51VZA
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrUX51VZA.204:bd12/03/2012:svnASUSTeKCOMPUTERINC.:pnUX51VZA:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnUX51VZA:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:
dmi.product.family: UX
dmi.product.name: UX51VZA
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.91-2
version.libgl1-mesa-dri: libgl1-mesa-dri 18.0.5-0ubuntu0~18.04.1
version.libgl1-mesa-glx: libgl1-mesa-glx 18.0.5-0ubuntu0~18.04.1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.6-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:18.0.1-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20171229-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2
Status changed to 'Confirmed' because the bug affects multiple users.