Image preview resize mode must be valid
Saving Image Mod settings failed because image preview size mode was not one of: auto, standard, custom, or original.
Why this happens
Admin-only validation on image_preview_size_mode (UI may say “resize mode”). Invalid values at runtime fall back to auto; this error appears on save. Custom mode also needs width/height in range.
Diagnose and fix
1. Admin → Settings → Mods → Image Mod — pick a valid mode and save.
2. For custom: set width/height (typically 64–4096; height may be auto).
3. Do not POST arbitrary strings via API scripts.
4. Downloaders never see this message.