Open a big enough presentation, then click on 'Fullscreen presentation'. There is a spinner that is displayed from the moment you clicked the button until the slideshow.svg is generated by the LibreOffice Online backend ('onSlideDownloadReady' function from 'loleaflet/src/map/handler/Map.SlideShow.js'). The problem is that is the presentation is big enough it will take a while until it is downloaded and displayed by the browser, meanwhile the user will see a blank screen.
Fixed via https://gerrit.libreoffice.org/#/c/70250/
Alexandru, as a suggestion, if the first line of the commit message contains a bug number in a format like "tdf#" plus the number (eg. tdf#124544), there's automatic commit notification between gerrit and bugzilla. Noting the commit manually now, thanks for the fix! https://cgit.freedesktop.org/libreoffice/online/commit/?id=51e849bf5dcb4bcef1fd042bb45f07b4383cb461 author Alexandru Vlăduţu <alexandru.vladutu@1and1.ro> 2019-04-04 13:57:23 +0300 committer Szymon Kłos <szymon.klos@collabora.com> 2019-04-04 13:46:29 +0200 loleaflet: optimize slideshow spinner
Thank you Aron, I was not aware of this at the time!