To save time I figured I better output a simulation (lengthy enough), to IFDs first and then render them later god willing.
In Version 13.0 I set the file extension to IFD and started rendering.
Then through hcmd.exe I put
mantra -f IFDFile_001.ifd ImageFile_001.png
The errors given start with
Unknown command: PIC2<heart>

What is going on now?
I renamed the file to a PNG and a PIC and it won't open, so I don't think it's that.
The IFDs are also all exactly 5,463KB in size, which also seems odd, possibly insightful.

Apparently you set the IFD in
/out/mantra_ipr/soho_diskfile
not
/out/mantra_ipr/vm_picture

This is in the Main tab of a mantra node

I expect an error or at least a warning reported when doing it wrong IFD as Output Picture path file's extension.