In LO 188.8.131.52's Impress, starting the slide show with a second screen attached shows the presenter console on screen #1, but doesn't display anything on screen #2 (unchanged, desktop background still visible). With LO 184.108.40.206 this works as expected (slide shown on screen #2). Also reproducible with soffice --safe-mode.
Steps to Reproduce:
Environment: Ubuntu 18.04.2 LTS (amd64), KDE 5 with Plasma 5.12.7 (as shipped with Ubuntu), LO 220.127.116.11 "Linux x86_64 (deb)" from libreoffice.org, primary screen 2560x1440, secondary screen 1920x1200 extending the desktop rightwards (reproducible with other screens / resolutions).
1. Attach secondary screen, configure X.org to extend the desktop to the right (e.g. using xrandr, arandr, ...).
2. Run soffice 18.104.22.168.
3. On start screen: Create: Impress Presentation. Pick arbitrary template. Open.
4. Start presentation with F5.
Primary screen shows presenter console (current slide, next slide, notes). Secondary screen doesn't show current slide but continues displaying desktop background.
Presenter console on primary screen, current slide on secondary screen.
User Profile Reset: Yes
Build ID: aecc05fe267cc68dde00352a451aa867b3b546ac
CPU threads: 8; OS: Linux 4.15; UI render: default; VCL: kde5;
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Side note: Disabling "hardware acceleration" doesn't change the observations described.
Thank you for your bug report.
This seems to be the issue already described in bug 119719, so I'm marking it as a duplicate. The underlying problem has been fixed in Qt 5.10, so outside of LibreOffice itself. Ubuntu 18.04 only has Qt version 5.9.5.
Should your problem still be reproducible with a newer Qt version, please reopen this bug report.
*** This bug has been marked as a duplicate of bug 119719 ***