If you are getting this issue with the PDG workflow (using PDGAssetLink), then I suggest trying with the regular (non-PDG) path to rule out bugs with just the PDG workflow. The regular terrain generation differs from the PDG generation so it is possible for bugs (or missing features) to exist in one case, but not the other.
If you are specifying an existing TerrainLayer, I suggest trying another TerrainLayer with different size or properties. My gut feeling is that the SetAlphamaps error is a clue that not all is right in the internal terrain state. Note that since you are specifying an existing TerrainLayer, the plugin will just assign it to the TerrainData, and won't check if its compatible. Additionally, it might set some properties on the TerrainLayer if you have specified them via attributes.
Are you able to generate a TerrainLayer (via a new heightfield layer in H), and use that instead? If that works, then check that the sizes match between the existing and generated TerrainLayers.
If you can attach an HDA, I can take a look as well.
Thanks for the help.
So as per your advice we broke apart everything and tested it individually, NOT through PDG.
Turns out the U console error is from the very first HDA from a heightfield erode node and the layers it puts out (bedrock, debris, water etc)
So if we delete those with a blast, the error goes away BUT then we cannot process the chain later on. So the error disappears but then the texturing HDA doesn't seem to work properly with the input that's coming in that's missing those layers. (see attached initial hda - though I doubt it will be useful)
It's hard to debug this because in Houdini everything works perfectly. Even in the piped debug session.
Other things we tried: updating to HE 364.
One question that we are asking ourselves is if there is a problem with HDA's that contain both ‘regular’ geometry and heightfields?
Is there a way to get what node is problematic and a more specific error message? Read the debugging page (https://www.sidefx.com/docs/unity/_debugging.html) but again, since our problem does not show up in Houdini itself, but rather in Unity, it doesn't give us any insight.