Happens to me in 2018.1.5f.1

Still seeing this error in 5.6.1f1. Prankard's suggestion about disabling AspectRatioFitter did get rid of it for me.

I didn't see any actual negative impact from it, but I guess it's nice to know where the error is coming from.

Still having this issue in 5.6.0f3

Not fixed!!

So, I've had the bug recently in my project.
And it happens when:
Creating/Applying/DraggingDropping a prefab with the 'AspectRatioFitter' component in it.

Which sucks, because I had a massive menu prefab, with a few of these in, I use them to help layout the 2d assets on multiple devices.

Anyways, if people with this issue could try disabling the aspect ratio fitter on the component and let me know if it works.
What I've done is disable all the aspect ratio fitters, and then in code. Enable them upon creation of the prefab.

Here is a tiny editor script I wrote to help enable/disable and find all AspectRatioFitters and check how many aspect ratio fitters exists on a selection.

using UnityEngine;
using System.Collections;
using UnityEditor;
using UnityEngine.UI;

public class EditorFix : MonoBehaviour
{
[MenuItem("Fix/Check All Aspect Ratio Fitter")]
public static void Check()
{
GameObject activeGO = Selection.activeGameObject;
AspectRatioFitter[] arfs = activeGO.GetComponentsInChildren<AspectRatioFitter>();
int onCount = 0;
int offCount = 0;
foreach (AspectRatioFitter arf in arfs)
{
if (arf.enabled)
onCount++;
else
offCount++;
}
if (onCount != 0 && offCount != 0)
{
foreach (AspectRatioFitter arf in arfs)
{
if (arf.enabled)
Debug.Log("On : " + arf.gameObject.name);
else
Debug.Log("Off : " + arf.gameObject.name);
}
}
Debug.Log("Aspect Ratio Fitters, On: " + onCount + ", Off: " + offCount);
}

[MenuItem("Fix/Turn On All Aspect Ratio Fitter")]
public static void TurnOn()
{
TurnOnAspectRatios(true);
}

[MenuItem("Fix/Turn On Off Aspect Ratio Fitter")]
public static void TurnOff()
{
TurnOnAspectRatios(false);
}

private static void TurnOnAspectRatios(bool on)
{
GameObject activeGO = Selection.activeGameObject;
AspectRatioFitter[] arfs = activeGO.GetComponentsInChildren<AspectRatioFitter>();
foreach (AspectRatioFitter arf in arfs)
{
arf.enabled = on;
}
Debug.Log("Turned " + (on ? "on" : "off") + " " + arfs.Length + " AspectRatioFitters");
}
}

Happened to me right now. If it is resolved, where is the solution?

"Voting disabled for resolved issues"

This is NOT resolved. Still happens for me in 5.0.1f.

I assume it's not damaging but it's annoying to see it in console everytime I drag UI prefab to scene.

Still an issue in 5.0.1f1 :(

Nevermind. Just reported the bug using the official Unity bug tracker, which I did not know of when I posted that last comment. You should always use that! Menu: Help -> Report a bug

I don't understand how but this is still an issue... I have a picture I would like to post of the problem but that can't be done in the comments section here. I'm going to post it on the message board instead.