The slideshow resolved its image as preview_url || hero_url || url. preview_url is only emitted when lightbox_preview_enabled is on (default false), so a default install fell through to hero_url — the 1920x1080 fit:'cover' centre crop built for gallery header banners. object-fit: contain then letterboxed an already-cropped 16:9 frame, so portrait photos lost their top and bottom and 'Black Bars (No crop)' looked inert.
Emits slideshow_url (same aspect-preserved preview tier) unconditionally for image photos; the show prefers it and never falls back to hero_url. preview_url stays gated so the lightbox opt-in is unchanged.
Fixes#1015.
Paul Nothaft