IBIS & Vintage Anamorphic: Diagnosing Jello/Warping?

Hey everyone,

I'm a gaffer usually dealing with the other side of the lens, but I'm trying to troubleshoot a problem on a personal project. I'm shooting with an ALEXA Mini and a beautiful old LOMO Squarefront anamorphic lens, and I'm seeing a noticeable 'jello effect' or warping, especially on horizontal lines, when there's any camera movement. My first thought was IBIS, as the Mini doesn't have it, but the rental house specified it was an ALEXA Mini LF, which does. I've tried turning IBIS off in the camera settings, but the issue persists, albeit perhaps slightly less pronounced.

Could my vintage anamorphic and the modern sensor be clashing in some fundamental way? What are the initial steps you guys would take to accurately diagnose this? Is it definitely an IBIS residual effect, or could there be something else at play with how the anamorphic elements are interacting with the sensor readout? Any thoughts on where to start would be appreciated.

Thanks, Jason