The issue I was running into was from Fusion Imposer 13.1.2, the Infinite stack function in the Step and Repeat module, Acrobat Pro build_2023.008.20423.
My apologies, my initial question did not detail the specific part of Imposer I had issue with. The infinite stack was being ignored, in both legacy and newly created .fpi files in FP build 13.1.2. Acrobat Pro build_2023.008.20423 seems to be a real problem with other Plug-ins as well, specifically Pit Stop Pro. I uninstalled Acrobat and re-installed version Adobe Acrobat 2020. Everything works as expected now. I have not tried to update Fusion to the latest build just yet, but will once the critical jobs are out and I can have some cushion time to un-install if needed.