As you can see, the object is perfectly aligned with the cube, during Edit mode. But when i click the Play button, it reverts to the original import state:
I want my character to keep in the rotation 270,0,0, and not flip to that weird number. I tried reimporting and deleting/replacing my prefab, with no success (If that helps, the parent is rotated 270 degrees in Y axis, and is not linked to anything else). I have a clean scene, no scripts or nothing (yet), i can’t figure what’s going on!
If you don’t have an animation component on your object, did you try applying your rotation modifications to the prefab?
Make sure to only make modifications when preview mode is disable. All modifications made in preview mode are discarded after it.
Somehow Unity re-added the Animation Component and it was causing this error (because of the way i imported it from Blender). Thanks for all answerers.
open your object in blender and select all in that object. then press Ctrl+a (apply) then select rotation. it resets all rotations to 0 but your object dont rotate. so now unity can understand how your object is ment to be. hope this helps 
I noticed my Object jumps to an X Rotation of 270 degrees, but only in animated
Cheap and dirty workaround:
- rotate the object 270 degrees on X axis so that the orientation doesn’t change upon animation
- make the object child of an empty, then transform the empty to your desired rotation/position
it can be happening because of for reasons u may have java script component/function that get executed when u play run and finally modification of ur xyz rotation occure