I believe I may have found a bug with the rotation gizmo.
If I have a mesh with a previously set quaternion rotation, and then attempt to use the rotation gizmo on that mesh, I am getting this in the console: Uncaught TypeError: c.attachedMesh.rotationQuaternion.toRotationMatrix is not a function
I am not sure if I am doing something wrong, or if this is a legit bug.
Here is a demo I adapted from the GizmoManager example: https://www.babylonjs-playground.com/#4TBMBR#28
(All I changed was adding line 13. Just try to rotate any of the spheres)