'Generate Bump (Height) Map' producing randomly darker/lighter results in ps2020

I'm trying to generate height maps for a sequence of rendered frames from an animation of a face in Maya 2020.

I'm doing this by loading the images in EXR format into Photoshop 2020, and calling the 'Filter -> 3D -> Generate Bump (Height) Map' tool. The settings for the tool are exactly the same each time they're called, however the results vary in overall darkness between frames. Frames randomly appear lighter/darker than others. The difference is subtle, but will cause huge issues later on in the workflow if not fixed. See the attached images for a sample [Actors face covered up so I don't get in trouble at work :)]

The exact same EXR frames ran through the same filter with the same settings in PS 2018 does not produce this issue, but I need this process to work in 2020.

I suspect its some kind of color mode issue, but no matter how many settings I tweak, nothing changes at all.

Anyone have any ideas what might be causing this?