Extremly slow slide show on empty presentation

When I open LibreOffice Impress and try to start the slide show on the empty 1-slide-presentation, the UI freezes for 20 to 40 seconds before the slide is shown. During this time no input is possible. The same thing happens with any other presentation. During the slide show, whenever I try to go to the next slide, it takes 5 to 10 seconds and the screen flickers. Editing slides is no problem at all.

I have the same behaviour with both LibreOffice Impress and 6.1.5. I tried to change the memory settings for the image cache (1000MB total, 50MB per object, 50 objects cached) which had no effect. I also tried to activating/deactiving hardware accelaration/OpenGL, but it also does not have an effect. Trying to change slideshow settings also had no effect.

What could be the reason for this behaviour? What could I try to be able to play any slides?

My system: Debian Stretch (stable), 64bit, with freshly installed “libreoffice” package via APT (LibreOffice, same issue when instead the Stretch-backported “libreoffice” package (LibreOffice 6.1.5) is used