The Online/Offline sidebar icon was always shown, even on an install with no data/offline.pmtiles — offering a choice that can't actually work. LayerToggleControl#remove() removes the icon (and hides its panel) once the existing /api/offline-tiles check confirms there's nothing to switch to; a transient failure of that same-origin check leaves the switch as is rather than guessing, since that's the request itself failing, not evidence offline tiles are unavailable.