Have you selected a server action under the form?
I was about to report a dropzone bug but found the issue.
If the form has no action (server connect action) defined, it will throw an error on console and no elements are displayed on the dropzone area.
You should have explained this in your bug report. Please when reporting bugs make sure to explain the problem as clear as possible, as only saying “It doesn’t work” does not really help us identify the issue.
When I check the dropzone thumbs option, I can see the files and their names in dropzone. But when I uncheck the thumbs option and then select the file, nothing changes. No file is added to the dropzone and its image remains completely untouched. File is not added to dropzone. Normally we were seeing our filenames always inside the dropbox.