I’m running into a problem when using my HDAs in Unreal Engine 5.6 with Houdini 21.0.
When I drop my HDA into UE, none of the nodes seem to process at all. The only way I can get results is if I enable Session Sync and then recook inside UE.

Has anyone else run into this, or know if something changed in the way cooking is handled?

Works fine for me without Session Sync when using spline actor in the World Input of the HDA.

It may be due to a Houdini/Houdini Engine mismatch. You can verify in unreal under HoudiniEngine>Installation info panel.

Make sure you are using Houdini Engine Indie With Houdini Indie.

Did you ever figure out this issue? I'm having the same issue in UE 5.7

Okay it was a licensing issue. To expand on what ShootingBLIND recommended, when I looked at HoudiniEngine -> Installation Info in UE5, the License Type Acquired was "Houdini Engine for Unreal/Unity", which is not the appropriate one for Houdini Indie. I went into my Licence Administrator, got rid of this license, and got the Houdini Engine Indie license from https://www.sidefx.com/services/licenses/ [www.sidefx.com] . I was getting issues downloading the license through the license manager itself because of the known bug on 21.0.559, so I followed these steps (https://www.sidefx.com/faq/question/i-am-trying-to-install-licenses-but-receive-the-no-selected-servers-found-error-what-do-i-do/)

What plagued me, was even after removing this license and adding the new one, is UE5 still kept loading the old license, even when I deleted the temp files in Content/HoudiniEngine, as well as the the Intermediate and Saved folders from my UE project. However, as is typical of most IT problems, restarting my computer finally did the trick. Now when I open UE5 and recook a .hdalc node, it cooks properly, and the houdini engine indie license is referenced correctly in InstallationInfo