For the Houdini Engine for Unity plugin, there have been significant changes to how Unity terrain is generation from height fields, and also how height fields are generated from Unity terrain (as input). Most notably, the plugin now relies on use of Corner sampling, instead of the default Center sampling, for height field nodes. It also requires height field size and grid spacing values to be exactly power of 2. This will produce the best match in terms of size when translating from Houdini height field into Unity terrain, and vice versa.
Please see update documentation here:https://www.sidefx.com/docs/unity/_terrain.html#Terrain_Size
The plugin now ships with a sample HDA that lists the recommended parm values for height fields, located in: