That's me again, struggling with the animation. I created a number of key frames. However, my camera sometimes was doing a full 360 loop interpolating between two close camera positions. So I had to add more and more key frames to stop it. But in the end I have just one odd frame 114, where it suddenly jumps. In the "Transform" panel under "Rotations" I have "Quaternion (WXYZ)"). All the components of the quaternion are quite small and change its sign between these two frames as I see in the "Transform" panel.
Deleting the key frame 113 causes the camera to roll all over the place again.
Is there a way to stop this behaviour? I also found some posts talking about parenting when creating animations, but I can't understand it exactly.
I checked how it looks in the Graph editor, but rotations are smooth and no sign change at that frame 114. So as far as I understand Graph Editor has rotation in local coordinates, while the transform panel in global.
The animation is here (model from blendswap, made by TheDuckCow):
Here is an example. This frame is fine.
Apparently something numerical happens when they all go through zero...