There are 4 ways following which we can reproduce this bug. They are mentioned in Scenario 1, Scenario 2, Scenario 3, Scenario 4.

Scenario 1
Generating automatic animation from UI button throws EndLayoutGroup error.

Steps to Reproduce:
1. Create a new project.
2. Component > UI > Button
3. Select "Animation" from Transition dropdown
4. Select "Auto Generate Animation"
5. Select "Save" or "Cancel" from save dialog.

Scenario 2
This issue also occurs on changing "Scripting Runtime Version"

Steps to reproduce:
1. Create a new project.
2. File > Builds Setting > Other Settings > Scripting Runtime Version > .NET 4.x Equivalent
3. "Restart Required" pop up will appear.
4. Select "Cancel"

Scenario 3
This issue also occurs while setting "Log Path" from Log Preferences of ProBuilder.(Only on mac)

Steps to Reproduce:
1. Create a new project.
2. Import "ProBuilder" from Package Manager.
3. Tools > ProBuilder > Debug > Log Preferences.
4. Select button which sets Log Path.
5. Select "Cancel" or "Choose" from ProBuilder Log Directory.

Scenario 4
This issue also occurs on applying modified Avtar mapping settings.

Steps to Reproduce.
1. Create a new project.
2. Import a 3D model.
3. Select imported model in project tab.
4.Rig > Configure > Mapping
5. Make some changes in Body of 3d model
6. Edit > Undo Avtar mapping modified or Ctrl/Cmd+Z
7. Select "Muscle & Settings"
8. Select "Apply" from "Unapplied import settings"

Reproducible on:
Unity 2018.3.0a1, 2018.2.0b5, 2018.2.0b1, 2018.2.0a1, 2018.1.0f2, 2018.1.0b1, 2017.3.0f3

Working on:
2017.2.0f3

Environment:
Occurring only on Mac 10.13 and 10.12

Error Details
EndLayoutGroup: BeginLayoutGroup must be called first.
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)