Oh, dear. Latest dated 201217 gives this
Which I suppose comes from app: make "gegl:introspect" an optional operation dependency. · GNOME/gimp@2cae9b9 · GitHub and INSTALL: adding infos about `dot` for "gegl:introspect" dependency. · GNOME/gimp@d90d622 · GitHub
These appimages are excellent tools, aferrero deserves recognition for the work done to continuously supply the latest and greatest. Pity about GEGL being a hurdle yet again.