A rigid-body registration workflow works wrongly in 2D instead of 3D

[micgriffa]

Dear Elastix/SimpleElastix developers/users,

we are encountering a very unusual behavior in a rigid-body registration workflow implemented with in a Python script using SimpleElastix.

You can find attached the input parameter set file:
Parameters_RigidBody.txt.
The Python script can be downloaded from here.

The fixed image can be downloaded from here.
The moved/moving image can be downloaded from here.

Both are 3D, uint 16-bit, single channel, single time point images in TIFF format.
They are X-ray attenuation contrast tomograms obtained with a laboratory tomograph.
ATTENTION: TIFF file size of the order of 4.5 GiBytes.

Instead of working in 3D, the registration workflow occurs only in 2D.
That's very strange because the same workflow, with the same input parameters, has been working very well, in 3D, on other
sets of similar 3D images obtained with the same tomograph.
We can't understand why that's happening.

We are running the registration workflow on a workstation with Ubuntu 20.04.4 LTS with a build of SimpleElastix Ver. 2.0.0rc2.dev910-ga138e (ITK 5.1).

We would be great for any suggestion of where to look for such a weird behavior of this registration workflow.

Thanks a lot.

Best regards,

Michele Griffa