Hey Alex.
See below for the full error log. Can also repro it fairly easy with what I did above
ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) (at <eae584ce26bc40229c1b1aa476bfa589>:0)
System.ThrowHelper.ThrowArgumentOutOfRangeException () (at <eae584ce26bc40229c1b1aa476bfa589>:0)
UnityEngine.EventSystems.EventTrigger.Execute (UnityEngine.EventSystems.EventTriggerType id, UnityEngine.EventSystems.BaseEventData eventData) (at C:/Program Files/Unity/Hub/Editor/2020.2.7f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventTrigger.cs:218)
UnityEngine.EventSystems.EventTrigger.OnPointerDown (UnityEngine.EventSystems.PointerEventData eventData) (at C:/Program Files/Unity/Hub/Editor/2020.2.7f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventTrigger.cs:257)
UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerDownHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/Program Files/Unity/Hub/Editor/2020.2.7f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:36)
UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor) (at C:/Program Files/Unity/Hub/Editor/2020.2.7f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:262)
UnityEngine.EventSystems.EventSystem:Update() (at C:/Program Files/Unity/Hub/Editor/2020.2.7f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventSystem.cs:385)