I could work around this strange behavior with quick fix in the past but it's happening again and I 'll have to dispatch lots of elements in several scene tonight and tomorrow so i'd really like to find the silver bullet.
I have a few planes facing the camera, dispatched on the z axis as follow:

front elements are a river scenery
Back elements are a waterfall and stuff
and the few layers behind the coco trees are all mountains and hills
The move is a dolly out from my characters which are positioned in the shot at the level of the back elements but in a separate group above everything in my layer window. The end position is a wide shot of the whole scene.
So it's supposed to be a cool track-out where I of course want to play with perspective.
Everything's fine as long as I don't tilt and pan. But I really want to start from a panned position cause my characters are on the side of the frame and it allows to reveal some cool things on the way to the wide shot.
Here's the pb: everytime I 've been panning in camera moves in previous scenes and this one, some plates at times randomly pop up in front of the one closer to me for no reason.
- Each layer are neatly placed in z (0, -1, -1.5, 2, 3 etc...)
- The only depth sort I activated is the main plane (sort by depth).
- All items in subgroups have their z at zero
- I didn't activate "rotate to face camera" whatsoever
So I can't figure out what's the issue.
It only happens with pan/tilt, which in all logic should not occur cause the layers are supposed to stay still neatly stacked in order on z, no matter what the camera does.
It's even more obvious when orbiting with workspace tools. I invite you to do the test yourself. As you change view point, back layers decide randomly to jump in front of others and then jump back for no apparent reason.
Can anyone help me here?