SUMMARY
Generically, a drag of a tree node or a tag node etc in the tree works as it should- select, drag up or down, and if you approach top or bottom of the control window, the window scrolls continuously. In Thumbnail mode, where if you have say 2 images that you want to group via a drag-over, and where those images are separated whatever- 50 other images due to naming or sorting preference etc- a drag of a file to the control boundary yield a nudge in that direction, but not a scroll. So, you have to back off and move down again. The nudges are tiny- 10 pixels etc, so moving a full row can take 50 cycles, and multiple rows- forget it. Easier to create a subfolder, move the files there, group them, and move them back to the parent folder. 


STEPS TO REPRODUCE
1.  In Thumbnail view, find a folder that has enough images to yield something like 3+ pages of images
2.  Select any image from any row on the first page of thumbnails, and commence a drag op towards any image on the 3rd+ page
3. As you approach the frame's bottom boundary, you will see the images on page 1 nudge up a bit and stop. 

OBSERVED RESULT
As with #3 above, page nudges up, but doesnt move continuously

EXPECTED RESULT
Page should scroll up, as is typical with any file manager, since doing a mouse-click-drag on the scroll bar control by defintion is not compatible with holding a selected image in drag mode

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Its possible this is some user setting/config thing, but if it is, I cannot imagine any scenario where this would be beneficial. And, its not consistent with how the Album or tag trees work, or how file managers/explorer work.