Looks like the Houdini interaction is broken in the last few builds. From what I can see Houdini seems to write the input data ok, Gaea then executes the script but does not write the .r32 output file(s). 18.104.22.168 works fine.
The incompatibility with the Houdini bridge has been fixed. Run Gaea to let it patch the issue, or download from here: https://gaea.community/d/295-gaea-1218-production-ready