Andy, Waxings:
This slight jello is caused by vibration which cannot be absorbed by rubber dumpers.
On my P3P, usually none, but putting sun shade (3D printed, approx. 4g) causes unbalance of gimbal and jello occurred. Also on strong wind day (> 15kts), or rapid descending.
I think, balancing props or change hardness of rubber dumper will improve the vibration (although I haven't tried by myself). That was effective on my P2 + GoPro.
P.S. As some people wrote above, high FPS will effective to decrease jello, but still blur remains - a same object is at different pixel on previous and next frame. Also ND filter (lower shutter speed) is effective, but also blur - only band width of rolling shutter becomes wider. If post processing could remove jello, also resolution lowers. Basically, to take advantage of precision of 4K video, defeating vibration is the only way, IMHO.