Created attachment 372322 [details]
screenshot displaying Gimp 2.10 error messages when trying to open files on another partition.

In my experience, Gimp 2.10 will not open, save or recognize files which are

(1) in directories referenced by symbolic links, the ones you create in linux with the ln -s command

(2) in directories located on partitions other than the root partition on which Gimp 2.10 is installed.

(3) on USB sticks which are otherwise properly mounted and visible to other applications such as Libre Office.

I just installed Ubuntu 18.04....  In the screenshot attached you can see on the right side of the screen the graphical file manager focused upon a directory located in /dumpster my data partition.  I have selected 3 files and told the system to use Gimp 2.10 to open them, and you can see the 3 error messages. Gimp 2.10 says the relevant directories and files do not exist.  I tried relocating them to a usb stick, and Gimp cannot see them there either.  

The directories in that partition are also referenced under my /home directory as Documents, Pictures, Music, and Downloads, but Gimp 2.10, unlike its predecessors cannot see the directories or their contents, either as symbolic links under /home/bruce or in their actual location at /dumpster/bruce 

I had to move the files to my desktop to be able to work on them. This is pretty bad, as my root partition is an SSD with limited space.