Hello Martin, how are you?
Please, first of all, remove all public link from this thread.
We have a very strange issue here: it happens only on Android platform (all Android platform) and Facebook app (so I mean: Facebook on Chrome or other browser works fine).
Video loaded with Facebook app browser fails (only on Android), error message is:
html5: Video file not found
Couldn’t find the required video type: video/fv-mp4
We did try with and without preroll ADV. Audio is not available in all cases. With preroll… you can see preroll video but not the following video. Without preroll you can see the video (but without audio), so I suppose first video is always displayed (but without audio in all cases).
You could try here: (please remove) choose one of video post.
May you please take a look and save us?