"QuaternionToEuler: Input quaternion was not normalized" is printed in the Console all the time

"QuaternionToEuler: Input quaternion was not normalized" is printed in the Console all the time whenever the scene is opened and any input is registered (e.g. clicking on anything in the Hierarchy).

I have all of my Cameras and Timelines as nested prefabs inside one prefab: Prefab_CamerasAndTimelines.

This gets solved by opening a Timeline asset that is in that scene and then simply closing the animation Window.

I have tried isolating where the problem comes from. It has to do with the Timeline or the MainCamera.

Trying to replicate this in a different scene did not work, after placing Prefab_CamerasAndTimelines into the scene nothing happens.

I then rebuild the Scene and once all references have been assigned the problem started reoccurring.

Please help

 

I just had the exact same problem and solved it.
(2021.3.0f1)

I had a camera manager prefab with the main camera and virtual cameras tied together.

Errors began to occur while working on the camera, and even after rebooting the editor, they did not disappear.
I wasn't using the timeline.

Looking at this article,
I guessed that something was wrong with the prefab where the camera was used.

I reverted Prefab, and Setting again (same value)
The error disappeared.
so I can't figure out more about the cause,
but... I think there's something wrong with Prefab

 

Thank you, I was working on camera-stuff and got this error when I opened a different scene (that used my camera prefab). I had to 'revert' any overrides on my camera prefab instance in that scene to fix it.