Alt hold climbs or descends with yaw input

I have looked everywhere for a solution to this problem: Tri-copter flies perfectly in stab mode. When switched to Alt hold, the copter is holds alt very well, but as soon as I yaw to the right slightly, the copter descends, when I yaw to the left the copter climbs. After each, the copter remains at the new altitude.
I have calibrated using “compassmot” several times with little effect. Any suggestions where I should start to solve this problem?
Thanks for any help.

Providing tlogs and data flash logs will help to troubleshoot your issue.

I have discovered that things work perfectly in the evening, but go wildly crazy in the bright sunlight. Baro readings in the sunlight were very erratic. I decided to see if covering the barometer with black tape would help, and this seems to have solved the problem. Perfect loiters and altitude holds even in very windy conditions.