With KPACS and EFILM, I guess it gets the images by DICOM Retrieve not by http GET (WADO).
If Weasis build the WADO url for downloading the images, it means weasis-pacs-connector works correctly (get the image references by DICOM C-Find).
I am surprised that you have this problem by upgrading Weasis 2.0.3 to 2.0.4 because there is no modification in the class which handles the WADO URL and connection. Have you tried to rollback to 2.0.3?
In the http connection, I don't understand from where comes the cookie reference. Is there a cache in the WADO service?