I also am having the same issue attempting to edit pictures in Dropbox using Photo Gallery.  Until recently you could select a photo anywhere on your computer including Dropbox then double click to open with Photo Gallery or Right Click and select Open With Photo Gallery.  Once done in the upper left corner of the screen you would select Edit and Manage Photos and the folder containing the selected photo would open in Photo Gallery displaying all photos in that folder including the selected photo and nothing more.  I did this daily and had no trouble accessing, displaying, or editing photos stored in Dropbox using Photo Gallery.

Now if I select a photo stored in Dropbox, double click or right click and Open with Photo Gallery, every picture on my computer displays and is totally unrelated to what I selected, has no organizational method to search and find the selected picture and even includes jpeg documents I have scanned.

There is a list of folders on the left side and Dropbox is not an option to select and it is unclear to me exactly where Photo Gallery is getting this list from, because everything on my computer is saved in Dropbox and everything I work on whether it be a document, jpeg scan, photo, music or anything else is done in Dropbox.

This is completely unacceptable as I have thousands of pictures on my computer and it is important to be able to track the location where photos are stored like in a directory, access them and edit.

This was a simple process until I upgraded to Windows 10 Pro.  I do not know if it is related to this upgrade but this should be a simple task for a MS Operating System to handle as it did before for many years without any problems at all.

If anyone has an idea or explanation how to remedy this I would be greatly appreciative for your assistance.

Thank you