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.