What am I supposed to be looking at in the video? It looks and sounds like several seconds of handheld video, which was shot on a fairly windy night.
I saw that. It is a handheld shot. I do not see anything that strikes me as unusual. If you have Digital IS turned on, then the image may get cropped slightly.
While true that some stabilization systems crop the image, that's not what is being shown in the video. The buildings on the left-hand-side indeed have a wobble (jell-o) effect going on. A shaky hand-held shot no doubt causes it's own set of issues, but this is an additional problem above and beyond.
Yes, I don't have Digital IS turned on, just Lens IS + IBIS. Apparently, after doing some research the wobble is caused by IBIS. And it seems the majority of people who reported are using RF15-35 trying to shoot wide-angle below 20mm. I'm just trying see if my gear has problem or it's working as expected.
I don't have any equipment with IBIS (the EOS C70 uses either lens IS and/or digital stabilization), so don't have first-hand experience. I can state though that for the specific equipment itself, I'm not a fan of any non-optical solution. I do like the different rigs you can get which seem to offer much better (and sometimes superior) stabilization solutions.
It is shot in the dark, using a wide angle lens, possibly without any specific part of the image for a stable AF lock. Just what exactly should the IBIS be locked onto? As near as I can tell, nothing. The OP reports this only happens at the wide end of the lens, 24mm. It s working normally, IMHO.