Diagnosing 'Jello Effect' with Vintage Anamorphic and IBIS, Help!

Hey everyone,

I'm encountering a frustrating issue on a personal project and hoping some of you seasoned folks have faced this. I'm shooting on an FX9, pairing it with a beautiful old anamorphic lens, and I'm getting a noticeable 'jello effect' or warping, especially on horizontal movements. I suspect it's related to the camera's IBIS interacting poorly with the anamorphic's unique properties, but I’m not entirely sure.

I've tried recalibrating the IBIS and even experimenting with different stabilization modes, but the warble persists. It's most evident in tracking shots. I'm trying to figure out if it's purely an IBIS conflict, a rolling shutter problem exacerbated by the vintage glass, or something else entirely I haven't considered. I can't really dial back the anamorphic look, as it's central to the project's aesthetic.

What are the first diagnostic steps you'd typically take to pinpoint the cause of this kind of anamorphic jello, and what are the common solutions or workarounds you've found when IBIS and vintage anamorphics clash?