Long Delay when starting a slideshow in digikam using xmonad

If I use digikam (qt5 app, Version 5.5.0) under xmonad I have the problem that starting a slideshow has a delay of 30 seconds. In i3 and kde it opens without delay.

The problem is independent of which option for "screen placement" I choose in digikam settings. It is also independent if I use nvidia or nouveau drivers.

Same problem also if I start digikam "kdeinit5 digikam".

Same problem with gwenview instead of digikam.

Maybe there is already a workaround with specific xmonad settings.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xmonad 0.12-1
ProcVersionSignature: Ubuntu 4.4.0-91.114-generic 4.4.76
Uname: Linux 4.4.0-91-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
Date: Thu Aug 17 10:54:29 2017
InstallationDate: Installed on 2016-05-18 (455 days ago)
InstallationMedia: Lubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420)
SourcePackage: xmonad
UpgradeStatus: No upgrade log present (probably fresh install)