TAAAABB IT'S THE WHEELS! You were quite right! After seeing Adam's slo-mo its clear that the intermittent shake of that back leg must have been causing our wobble too. We did 3 mins with wheels and 3 mins without and there was plenty of difference! Oh the relief! Filming nothing in particular with that quality was almost better than filming the pier at sunset! I am going to fashion something to utilise both bolt holes on the bottom of the movi legs - solid but with hard foam underneath for some "give" when landing.