Jello and Yaw "Recoil"

[Witterings]

I'm getting quite a bit of jello which I used not to and also some yaw "recoil", if I put in right yaw, immediately I release the stick it corrects back to the left which makes keeping it in a straight line and videoing horrible.
My set up is an off the shelf DJI 450, Naza V2 with GPS and Zenmuse gimbal / GoPro black, the quads not been crashed, dropped banged or anything that should have made a difference to my knowledge.
The Yaw Issue.
Initially I miss interpreted what the yaw recoil was thinking it was just unwanted yaw and tried correcting by moving the GPS puck and re-calibrating and it made no difference. I've now tried a number of different "recommended" gain settings including I think going back to my original default settings and again it does nothing to improve it. If I yaw to the left and release it's smooth and doesn't do the same thing.

The Jello.
I used not to get it with 4s battery and 9 x 5 props, (recently running 3s and DJI 10 x 3.8's) I've recently tried switching back to the old set up and it made no difference am still getting the jello.
I've tried balancing all the props, I've also "tried" balancing the motors using a vibration meter on a tablet sitting on the arms (one motor at a time) but I couldn't really see that any of them seemed to be noticeably "out".

I'm not sure of the 2 may be connected in any way and hence posting in the same thread as probably better to look at "The whole problem" rather than part in case they're interlinked at all, any thoughts / suggestion of what else I can try would be appreciated.
Not really sure which way to go and what else to try from here so really would appreciate any help / input people may have.