The changes introduced via
GUACAMOLE-249 allow the guacamole-server build to automatically detect the correct location for FreeRDP plugins. This removes the need for users to manually create symbolic links after building guacamole-server, but causes issues with the Docker image build due to the way a separate builder image is used.
The guacd Docker image build process expects that absolutely all build artifacts will be installed beneath /usr/local/guacamole, but this is no longer the case by default due to the above. With the FreeRDP plugins being installed outside /usr/local/guacamole, the plugins are not copied from the builder image, and support for RDPDR, RDPSND, etc. cannot be loaded when the final image is used.