I have the same problem in UbuntuStudio 19.04 on the new church computer. UbuntuStudio 19.04 uses the XFCE environment.
On the taskbar appears 3 windows (Projection Window; Quelea 2020.0 and Video). The content is projectable only if we click on the Projection Window. If we want to make changes to any song, the projection disappears.
Here my quelea-debuglog:
dez 24, 2019 1:16:45 PM org.quelea.services.languages.LabelGrabber
INFO: Using languages file /snap/quelea/651/jar/languages/gb.lang
dez 24, 2019 1:16:45 PM org.quelea.services.languages.LabelGrabber
INFO: Setting en-uk locale
Dec 24, 2019 1:17:13 PM org.quelea.windows.main.Main start
INFO: Started, version 2020.0
Dec 24, 2019 1:17:13 PM org.quelea.windows.main.Main start
INFO: OS name: Linux
Dec 24, 2019 1:17:13 PM org.quelea.windows.main.Main start
INFO: Using JAVA version 1.8.0_222
Dec 24, 2019 1:17:13 PM org.quelea.windows.main.Main start
INFO: 64-bit: true
Dec 24, 2019 1:17:22 PM org.quelea.windows.multimedia.VLCWindowEmbed lambda$new$2
INFO: Video initialised ok
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Oxygen-Bold.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Oxygen-BoldItalic.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Oxygen-Italic.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Oxygen.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/RobotoMono-Bold.ttf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/RobotoMono-BoldItalic.ttf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/RobotoMono-Italic.ttf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/RobotoMono-Regular.ttf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Vegur-Bold.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.FontInstaller lambda$setupBundledFonts$0
INFO: Loaded bundled font /snap/quelea/651/jar/icons/bundledfonts/Vegur-Regular.otf
Dec 24, 2019 1:17:41 PM org.quelea.services.utils.UserFileChecker checkUserFiles
INFO: Checking user files
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Number of displays: 2
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Mobile lyrics disabled
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Remote control disabled
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Auto-detect servers disabled
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Starting projector display on monitor 1 (base 0!)
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 run
INFO: Hiding stage display on monitor 0 (base 0!)
Dec 24, 2019 1:17:41 PM org.quelea.windows.main.Main$1 lambda$run$8
INFO: Loading bibles
Dec 24, 2019 1:17:41 PM org.quelea.data.db.HibernateUtil init
INFO: Initialising hibernate
Dec 24, 2019 1:17:43 PM org.quelea.data.db.HibernateUtil init
INFO: Initialised hibernate properties
Dec 24, 2019 1:17:44 PM org.quelea.data.db.HibernateUtil init
INFO: Initialised hibernate service registry
Dec 24, 2019 1:17:44 PM org.quelea.data.bible.Bible parseXML
INFO: Parsed bible: King James Version. Contains 66 books.
Dec 24, 2019 1:17:49 PM org.quelea.services.utils.VersionChecker getLatestVersion
INFO: Checking for an updated version…
Dec 24, 2019 1:17:52 PM org.quelea.windows.main.MainPanel
INFO: Creating schedule panel
Dec 24, 2019 1:17:55 PM org.quelea.windows.main.MainPanel
INFO: Creating library panel
Dec 24, 2019 1:17:55 PM org.quelea.windows.library.LibraryPanel
INFO: Creating library panel
Dec 24, 2019 1:17:55 PM org.quelea.windows.library.LibraryPanel
INFO: Creating library song panel
Dec 24, 2019 1:17:55 PM org.quelea.windows.library.LibraryPanel
INFO: Creating library bible panel
Dec 24, 2019 1:17:57 PM org.quelea.windows.library.LibraryPanel
INFO: Creating library image panel
Dec 24, 2019 1:17:57 PM org.quelea.windows.library.LibraryPanel
INFO: Creating library timer panel
Dec 24, 2019 1:17:57 PM org.quelea.windows.main.MainPanel
INFO: Creating preview panel
Dec 24, 2019 1:17:58 PM org.quelea.windows.main.MainPanel
INFO: Creating live panel
Dec 24, 2019 1:17:59 PM org.quelea.windows.main.MainPanel
INFO: Creating split panels
Dec 24, 2019 1:17:59 PM org.quelea.windows.main.MainPanel
INFO: Created main panel