Yes, I now also have the same problem.
I just upgraded to macOS 10.15.6 last week from macOS 10.14.6. using GarageSale 8.1.1 (1233).
In Editor mode I used to be able to select multiple images and drag them to re-arrange them. This DID work last week with macOS 10.14.6.
Now if I select multiple images in the image pane of the Editor Mode I can no longer drag the images. Dragging ONE image still works, but multiple images does not “pickup” the images and does nothing.
Neal