I’ve been using Tropy in the archives to record all of the metadata and then adding the photos in the evening. Somehow it appears that a few of the photo-less items somehow got mistakenly merged with items with photos. Tropy won’t let me click “explode item,” but it is also too far back in my work to be able to undo. I don’t understand how to undo it.
The explode item action is enabled only for items with more than one photo. If your item has only a single photo, you can right click on the photo in the photo panel and select ‘Move photo to new item’: this would create a new item, copy the current metadata and move that photo to the new item; if the original item contained only that one photo it will be a photo-less item after this.