I've been doing a lot of image work (digitizing vinyl LPs with covers/contents). As I'm working with the images, I sometimes open them in GIMP to fix issues (old vinyl albums have old covers and inserts). When I do this and save the "fixed" edited image by over-writing the previous bad version, Gwenview's Thumbnail Bar always shows the edited image (that is, the Thumbnail Bar appears to immediately reload the thumbnail when the image file is changed).

But, the main image display does *not* update. It continues to show the previous "unfixed" version of the image. I've navigated to other folders in Gwenview thinking that might force a image cache reload, but on returning to my LP image folder, Gwenview still shows in the main image display the image as it was when Gwenview first opened the folder.

The only way I've found to get the main image display to show edited images, is to close and re-open Gwenview.

This is ... annoying LOL

I've checked the manual and the key bindings and I don't see a "Refresh Cache" or something similar. Is there such a thing?

Don't worry be happy
Sometimes it does help to goto previous/next image and back again...

You can press F5 while Gwenview is focused to refresh the image. I agree however, I would like Gwenview to automatically refresh the image. I'm doing work with Graphviz+DOT and would like to see my diagram updates as I go along without having to ALT+TAB over and press F5.

Press F5 or add a refresh button to the toolbar.