(Plasma 5.4.1)
When using Dolphin to view folders containing photos (jpgs) the thumbnails show up perfectly. However, when deleting some of these photos and viewing them in Trash, only a very small percentage of those files have thumbnails, sometimes none at all.

Any idea what's wrong?

The most recent version of Dolphin (on KDE Neon) displays thumbnails for all images in my trash bin.