Try this to correct your tilted horizon issue.

I did the IMU calibration, then did the gimbal calibration while holding the gimbal level and forward, finally the gimbal calibration began on-screen with the 0% to 100% bar moving slowly (about 2 minutes) and it worked!!!!

I first sent my P4P in for repair due to roughly this error: “vision system requires calibration”.

At this time I did NOT have gimbal issues, the horizon was always good.

Over one month later I received a different unit back with no paperwork, no explanation. I had to be the one to contact DJI to get Refresh updated to the new SN. NOBODY at DJI will explain why I got a different unit back.

So this “repaired” unit now has the gimbal issue. It won’t maintain a level horizon. After several IMU / Gimbal calibrations, during which time the gimbal locked up pointing down and back. At that time chat support said ship it back and they’ll “expedite” it.

Long story short it was another three weeks before I got yet another unit back. During that time one of the supervisors, over the phone, told me he’d ship me a NEW unit OVERNIGHT. He quickly took back what he said about a NEW unit, but PROMISED to ship a replacement overnight.

The day that supervisor PROMISED me that I’d have the unit in my posession he sent me an email stating “And as promised we will provide a overnight shipping for you.”

The unit did ship that day, UPS GROUND. It took five more days for me to get it.

So now I have an obviously used P4P (the UV filter has small scratches in it) and the gimbal won’t stay level.

My symptoms?
Take off facing west and the horizon stays level if facing west or east. Face north and the horizon is tilted one way, face south and the horizon is tilted the other way.
ANY manual calibration just offsets everything. I can get it level north and south but then east and west are tilted.

I’ve done the IMU and gimbal calibration. My first unit did NOT have this problem! WHERE IS MY FIRST UNIT?

I chatted with TS once more and the guy said “send it in’. I insisted to speak with a supervisor because I had already sent it in twice. He kept presenting me with the repair form, I kept insisting and he finally said OK, a supervisor will contact you within 24 to 48 hours.

That was a couple of weeks ago and I've heard nothing. I am so disgusted with DJI. Support outright lies, I have it in writing. I agree with some other posters here, DJI seems to not (DOESN'T) care at all.

One poster said we need to tone it down. Huh? I’ve got over $2K in DJI equipment, bought the Refresh package, never crash my aircraft(s), and this is what I have to put up with?

I have a theory on why my first unit was replaced without an explanation: Someone at DJI realized it had a GOOD gimbal setup and used it for themselves or a VIP. NO ONE has offered an explanation, they just ignore my question.

ONE QUESTION: During gimbal calibration, what’s the gimbal supposed to do? Mine moves side to side a couple times and that’s it. It NEVER moves up and down during calibration, only during power-on. DJI support doesn’t even give me a straight answer to that, they only ask me “do you get an error?”

My gimbal calibration process failed at 50%. Phantom 4 Pro.

gustofusion Posted at 2016-5-12 08:38
https://www.youtube.com/watch?v=1j62sSSpjr4

This post is off topic.  It just shows images of tilted horizons.  There is a number of reasons for tilted horizons and a majority of them is caused by user error.  JC has a problem with his horizons snapping to different planes (I am guessing an HW issue).  Please watch his video.  This video is irrelevant and serves no purpuse other than for you to vet your frustration.  It's not helpful.   

Mabou2 Posted at 2016-5-13 13:00
Hmmm... mixed emotions in posting here.  My new P4 does have a problem with the gimbal staying out of level, and this problem only showed up after the most recent firmware update.  Also, the squeaking sound appeared as soon as the firmware update finished.  (How the squeak, which has been proven to be a poorly engineered wrapping of the ribbon cable, only appeared after the firmware update for so many people, is a bit of a mystery).  I don't see that "Tick" problem, just that my gimbal won't stay level for long.  Not a huge problem since pretty much all of my work is 1080P, so I shoot 4k then rotate a bit in post.  But still, shouldn't be an issue and will hopefully be fixable via firmware.

REALITY CHECK time... (note: if you want to just stay angry and complain, don't bother reading on... )

I totally agree with you.  People are so easy to jump on the negativity band wagon.
Support costs money.
Better/quicker support just means the drones costing more when purchased.
It did make me laugh when I read a post on this forum regarding DJI offering "DJI central", better/quicker support to commercial operations who may need it and are willing to pay for it.  Most users (who don't need it) complained it was too much and they'd just buy a new one instead.  This to me just shows DJI have a good business model.  Cost effective, cutting edge drones with (on average) effective support (people complain less when things go well).  
If the P4P cost $3000 with very good support I wonder how many would buy one?
Or if the P4P cost $4000 with excellent support would you buy one then?
I appreciate people are unhappy and have had bad experiences, however some of the posts here are just not helpful.
Maybe DJI should sell an S-Class model with excellent customer support (same drone, just go faster customer support strips) for those who can afford to spend more.
Thanks DJI, keep up the good work.

fanse29f7d45 Posted at 2017-5-20 09:00
I first sent my P4P in for repair due to roughly this error: “vision system requires calibration”.

At this time I did NOT have gimbal issues, the horizon was always good.

I would recommend starting a new thread.  Reading your post make me nervous about sending mine in, I look after it like it was my child, though I know some people (from watching youtube) don't care about their drones so much.  I wish you luck and hope you get it resolved soon.

Hi guys, I have a Phantom 4 Pro with the tilted horizon issue, I did the IMU Calibration and when I try the gimbal calibration, it doesn't finish, it gets stuck at 50% left it there for long time but I get no other option but power off and on again. Also tried reinstalling DJI Go 4 app and I get the same issue. Any lights on resolving this? thanks.