Recieved my DJI Osmo yesterday and I am really desapointed by its App. Indeed evey videos that I am shooting in 4K with an iPhone 6s+ are Jerky (see example here). Video shots using the Gimbal but with iOS Native video App are fine. It seems that the DJI App is not capable to handle recodring video in 4K.
Link here for example https://1drv.ms/v/s!Apw_JQYwYDvewhHuSxoqb1rerFwp (4K File available for DL) you will note that video seems to creat some kind of Jump Cut effet.
FIY this jerkiness problems ONLY occurs when recording 4K with the DJI App, HD is "jerk free" (As I said, the DJI App does not seems to be able to handle 4K)
Are you playing back the videos from your phone or from the Micro SD card? I would never use the videos stored on the phone as they are only for reference.
There is nothing official about this problem that I know of either, only a couple others on the forums have posted about this, it's only on 4k recording with this platform, like you said the rest of your HD recording etc is ok.
Hope they will fix this as I only shoot in 4K and I just sent back my G4S to China for reparation (GoPro Gimbal) and I need something to work in the meantime!
I can confirm that using 1080p and 720p on my Osmo Mobile in the DJI Go app works fine and that I see the 4k judder bug, however Filmic pro seems to work at 4k just fine.