Displacement Map Not Baking High Res Mesh Detail

[antmx]

I'm encountering an issue with displacement map baking, inconsistent between projects.

From one of my projects, here is a displacement map with distinct black and white detail.



Being confident with my workflow, my next project gives me very different results.  It baked the normal and occlusion maps very well, I know so since they took a long time to create, maybe 20 minutes (50m high res mesh baking onto a 650k  mesh), but the displacement map calculated in a fraction of the time, roughly 1-2 minutes, and looks totally different, no detail.



What is happening here?

My next step takes these meshes and textures into Substance painter.  On the concrete seating, the obvious black and white displacement map was visible and required very little adjustment to have an affect on the mesh texture, I don't really expect a flat grey to produce anything.  That detail on the mesh is very obvious, so why is it not baked?

[antmx]

To follow up on this, the very grey displacement bake did indeed contain height information after importing the mesh and textures into Substance painter, I'm unsure as top why the height data was not displayed as obvious black and white. 

However, after poly crunching and retopology of the model, then re-baking the maps from the high poly to re-imported low poly the displacement map was very visible, as expected.



In fact overall, the baked textures onto a retopolgised mesh looked better and rendered better than onto a medium-high poly triangulated mesh.