I’m also having this issue. I had an HDA working in engine, then made some changes that involved copying and pasting nodes into a new graph and setting up a “fresh” version of the HDA. In UE4 it builds just fine, but nothing shows up. Replaced all my nodes with just a primitive box, still builds, but no box in UE4. So I create a brand new Houdini file, make a new HDA that is just a box and saved it over my old HDA and rebuild it in UE4 and bam, there is a box now, even though the graphs were identical.
I feel like in my HDA there’s something that’s been “dirtied” under the hood, but it’s really difficult to troubleshoot what it is. Not sure what to do other than completely rebuild my tool in a fresh file.