When updating ACF fom 5.8.2 to 5.8.3 the media library’s grid view does not show any media. List view is ok. So adding media (e.g. featured image) to post/page is also not possible since it depends on media library grid view. Grid view is ok when ACF qTranslate is disabled.
“With ACF Pro activated, I can’t see media items in grid view (which means not at all when accessing them via the media uploader). Deactivating ACF Pro and the media items are visible in grid view as normal.”