I have my P2 connected to the iOS ground station, and it shows that my bird is climbing. It started at 1 foot, and is now at 21.4 feet. I haven't moved the P2 or touched it. Anyone having this issue? The phantom doesn't fly much longer than 5 minutes without dropping to the ground. Just replaced the MC, did a cold advanced calibration, and have charged batteries.

The barometer does tend to drift a bit, from heat I think. It zero's the barometer at every power up, but can drift + or - after that. It's not a precise measurement, however, the barometer is very sensitive to alt change which is why they hold altitude so well.

Phantom uses relative altitude. The barometer resets to zero at power up and displays altitude number, relative to the power up location. Unfortunately this number drifts a bit in the 15 minutes of flight time.

But, if ambient air pressure or temperature changes during your flight, it may no longer show as zero later upon landing in the same spot. The wind direction changes and it's no longer blowing hot air from the fields, but now it's blowing cool air from the lake. The sun sets or clouds roll in and the air temperature changes. All of those will affect the accuracy of the barometric altimeter.

That's why altimeters in real aircraft have a knob to adjust the altimeter setting to local ambient barometric pressure.

You have other issues if you are dropping to the ground in a 5 minute flight.

After it drops, it usually is able to fly normally again for another 5 minutes. I'm wondering if there's a radio interference between my fpv gear, ground station, and controller

Your controller is p2's on 2.4 ghz right. What is you FPV using. If the same band that could definately be an issue.

It is 5.8. Fat shark teleporter

Shouldn't be any interference issue your on different band widths. When you did the calibration did you first level your craft front to back and side to side with a level of some sort. The IMU calibration should give you stable hovering but don't think that's the issue with dropping. That sounds more like the altimeter or with the Phantom the barometer. That unit is built into the main board. How old is your Phantom?