I'm glad you have found the reason for the problem on your own computer and can now use a workaround (copy the gallery to a location outside of your Google Drive Sync folder and delete the 'desktop.ini' files).
However, I am still unable to replicate the problem.
There are 'desktop.ini' files within my own Google Drive Sync root folder and all gallery 'image' folders but it does not affect the functionality of JuiceboxBuidler-Pro. The presence of the 'desktop.ini' files does not make a difference in my own tests.
I think it's the desktop.ini that causes the problem.
Try manually deleting the 'desktop.ini' files from your Google Drive Sync root folder and all gallery 'image' folders to check whether or not the 'desktop.ini' files are the cause of the problem on your own computer.