The problem can also be reproduced in unreal editor, I added a message in their feedback forum about it.

Those problems are unavoidable, because infinite possible rotations result in the same resulting orientation.
Also euler, quat and matrix have different max angles for rotation. Within those limits the math should work.

However, those sign differences indicate you have a bug somewhere because i get back to the original values.

EDIT:
Looking at the 2 examples i've tried above, we see that column/major and rotation order can cancel out each other.
So my bet is that it's an left/right handed coordinate system issue you have - that would explain the signs.

Hi.

you could try Quaternion to Spherical coordinates then to Cartesian.