To reproduce:
1. Create an empty object.
2. Add Cloth component
3. In SkinnedMeshRenderer select Mesh and assign Capsule, Cylinder, Plane or Sphere. (most of the time, at least one of these meshes will trigger errors to appear)
4. Hover with mouse over Scene window.

Expected result: no errors.
Actual result: errors appear.

Notes:
Does not reproduce every time. But It happens most of the time, when assigning a new mesh, which was mentioned in the 3rd step.
Does not reproduce with Quad or Cube.

Reproducible with: 2017.3.0f1, 2018.1.0b5
Not Reproducible: 2017.3.0b10, 2018.1.0a5

Error in Unity 2018.1.0b5:
IndexOutOfRangeException: Array index is out of range.
UnityEditor.ClothInspector.GetMouseVertex (UnityEngine.Event e) (at C:/buildslave/unity/build/Editor/Mono/Inspector/ClothInspector.cs:933)
UnityEditor.ClothInspector.OnPreSceneGUI () (at C:/buildslave/unity/build/Editor/Mono/Inspector/ClothInspector.cs:1367)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.SceneView.CallOnPreSceneGUI () (at C:/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:2637)
UnityEditor.SceneView.DoOnPreSceneGUICallbacks (Rect cameraRect) (at C:/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:1322)
UnityEditor.SceneView.OnGUI () (at C:/buildslave/unity/build/Editor/Mono/SceneView/SceneView.cs:1697)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:291)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:284)
UnityEditor.HostView.InvokeOnGUI (Rect onGUIPosition) (at C:/buildslave/unity/build/Editor/Mono/HostView.cs:251)