Mouse clicks are not registered on plasma desktop

[joeyiscream]

After a computer (re)start and logging into KDE, mouse clicks not regiestering (fully). Windows can lose focus, but the clicked one does not get it. Keyboard and keyboard shortcuts work. Evtest reports mouse clicks, but xev only reports losing focus. Booting into Kubuntu Live USB - everything works as expected.

Current workarounds:
 - log out and log in again - that works most of the time
 - using gdm3 instead of sddm as window manager (cannot set autologin though, as it triggers the issue)

Ubuntu version: 18.04.1 LTS
Plasma: 5.12.7

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: sddm 0.17.0-1ubuntu7
ProcVersionSignature: Ubuntu 4.15.0-38.41-generic 4.15.18
Uname: Linux 4.15.0-38-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.4
Architecture: amd64
CurrentDesktop: KDE
Date: Sat Oct 27 18:12:16 2018
InstallationDate: Installed on 2018-08-28 (59 days ago)
InstallationMedia: Kubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
SourcePackage: sddm
UpgradeStatus: No upgrade log present (probably fresh install)

[joeyiscream (sgsghu)]

Probably related: https://unix.stackexchange.com/questions/369097/mouse-left-click-stops-working

[joeyiscream (sgsghu)]

Xorg.log

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Scarlett Gately Moore (scarlettmoore)]

This bug is very old, if it is still an issue please update the bug with information from a supported release.