I know there has been lots of threads on issues with the recent firmware 1.2.6. I too had a mainly unstable phantom but now all seems good. I performed a cold IMU calibration followed by an auto gimbal calibration https://youtu.be/kg0IB0XCiv8 (do this twice) and now after several tests all is good with my P3P on 1.2.6 with ipad mini 2, Pilot app 1.2.0.  No drifting - No instability - Level horizon - VPS hovers good - No lag or feed issues.

Another tip i found is after a successful compass calibration 'before take off' check to ensure the Phantom is pointing in the same direction of the radar pointer or the bird position in flight will not be in sync with the rc and app.

Perhaps this may help others. Also the fact that many report issues and many report no issues could it be related to a production batch of phantoms that just dont take the update well? I recieved my P3P on june 3rd (shipped may 28th). Maybe those still suffering problems are from an earlier or one of the first production runs??? Just a thought.

hmm interesting as i got mine in the same time frame as you have and i have been golden so far and the only damage was scratches on the landing arms after dropping it on the ground as it slipped from my hand while taking it out of my transport container.

There seems to be a lot of phantoms grounded since 1.2.6. I wonder are these earlier Phantoms?  

After the procedures you called out, with mine (later batch but came with 1.1.9), I cycled VPS off and on and rebooted the P3 several iterations and my VPS is solid as a rock.

Mine came with 1.1.9 too so perhaps this batch took the 1.2.9 better. Would be nice to hear fron owners who got earlier P3's with 1.1.8 or earlier. Definiely i had a little insatbility after updating but easily fixed with complete IMU calibration.

I received mine  on July 3rd. Not knowing any better, I did the update, but have not had a single issue since I got it.

-Brad

mphelan@pvpdigi Posted at 2015-7-24 07:41
Mine came with 1.1.9 too so perhaps this batch took the 1.2.9 better. Would be nice to hear fron own ...

Earlier birded FW. Imu calibration fixed strange flight behavior but did not remedy vps. just fyi

Anyone else find that a cold clibration resolved issues with 1.2.6 firmware? If not did you upgrade from 1.1.9 or earlier?  It maybe the latest firmware took well on top of 1.1.9 but not earlier versions.

I flew my P3P again today with zero errors or issues to report after installing the troublesome Firmware 1.2.6. As mentioned in the start of my thread I did experience some instability on first two flights after updateing but then did a cold IMU calibration and gimbal calibration. I have no issues whatsoever. Smooth flight, fully responsive, level horizon, no flyaway or erratic behaviour, hovers with vps solid, no video feed issues (to ipad mini2).
It's very strange that this version of firmware has caused so much heartache for so many but I am one happy pilot that I have no issues to report. Perhaps the cold calibration of the IMU did the trick! I got the tip from a youtube video which explains how the IMU (internal measuring unit) really controls everything....

mphelan@pvpdigi Posted at 2015-7-26 07:18
I flew my P3P again today with zero errors or issues to report after installing the troublesome Firm ...

Hi, I'm a newbe p3p owner.......gimbal overload error.....gimbal seems to be working.....gimbal never moves when I try to calibrate it......but comes back with gimbal calibrated after a few seconds.....I would have thought the gimbal should have moved to recalibrate itself?

ckb93@lycos.com Posted at 2015-7-27 03:40
Hi, I'm a newbe p3p owner.......gimbal overload error.....gimbal seems to be working.....gimbal nev ...

I found that it is a small rubber shipping piece that holds the gimbal caused problem - it works totally fine after I removed it.
I know this sounds silly, it is the white rubber with the red label "Remove before flight" -- I saw it at the beginning and I thought the warning is for removing the plastic holder so I removed that. Actually there are two things holding the gimbal in position for the safe shipment that need to be removed.

The DJI Firmware bugs are not limited to the Phantom 3 series. Check out the youtube videos on the DJI Inspire 1 crashes and see where DJI acknowledges "bugs" in the firmware updates.. My P3 Pro inherited a  slew of problems after the 1.2.6 update that were not there before..

Thank you all for the information I am new at flying drones but still decided to buy a good one right away.

ckb93@lycos.com Posted at 2015-7-27 04:31
I found that it is a small rubber shipping piece that holds the gimbal caused problem - it works t ...

I did not notice that piece until now either.  I thought same thing that sticker was for the clear plastic holder.  I am going out right now to see if that "Gimbal Motor Overload" is gone......HOPE

Thanks for posting!