Drones fly up and down in halt hold and loiter

Hello everyone, jo following problem, I hope someone is able to help me.
using a 2.6 apm I built a 6 engine with a frame in pvc that with the arms red and white to understand, I installed everything, voltage regulator, GPS, telemetry and receiver, I installed version 3.21 I have performed all the settings and configurations and unfortunately the drone-mode stable flies very well but as I insert mode alt hold or loiter begins to change height randomly and quickly making it almost impossible to control the machine, when in doubt I have already installed a version of the oldest firmware 3.15 without good results.

Then I proceeded to replace the engines and propellers in question were unbalanced, I performed the checks on the forum apm copter again without getting useful results attaching the diagnostic launched with the results returned.

among other things I tried to change apm 2.6 without anything changed

I hope for your help

Log File C:/Program Files (x86)/Mission Planner/logs/2015-06-15 08-40-00.log
Size (kb) 1256.4580078125
No of lines 19842
Duration 0:03:54
Vehicletype ArduCopter
Firmware Version V3.1.5
Firmware Hash 3c57e771
Hardware Type APM 2
Free Mem 1018
Skipped Lines 0

Test: Autotune = GOOD - [+] Autotune 4341-13186

Test: Balance/Twist = GOOD -
Test: Brownout = GOOD -
Test: Compass = GOOD - No MAG data, unable to test mag_field interference

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = NA -
Test: Parameters = GOOD -
Test: PM = GOOD -
Test: Pitch/Roll = GOOD -
Test: Thrust = GOOD -
Test: VCC = GOOD -

You need to provide an actual dataflash log.