To reproduce, open the attached project and open the UI Builder window. Notice the argument exception in the console:

ArgumentException: Requested value 'Right' was not found.
at System.Enum+EnumResult.SetFailure (System.Enum+ParseFailureKind failure, System.String failureMessageID, System.Object failureMessageFormatArgument) [0x00023] in <a35250a304174d009b77e5c5f6695f54>:0
at System.Enum.TryParseEnum (System.Type enumType, System.String value, System.Boolean ignoreCase, System.Enum+EnumResult& parseResult) [0x0017a] in <a35250a304174d009b77e5c5f6695f54>:0
at System.Enum.Parse (System.Type enumType, System.String value, System.Boolean ignoreCase) [0x00010] in <a35250a304174d009b77e5c5f6695f54>:0
at System.Enum.Parse (System.Type enumType, System.String value) [0x00000] in <a35250a304174d009b77e5c5f6695f54>:0
at Unity.UI.Builder.BuilderInspectorStyleFields.RefreshStyleFieldValue (System.String styleName, UnityEngine.UIElements.VisualElement fieldElement, System.Boolean forceInlineValue) [0x00dbb] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderInspectorStyleFields.RefreshStyleField (System.String styleName, UnityEngine.UIElements.VisualElement fieldElement) [0x0000f] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderInspectorLocalStyles.Refresh () [0x001bc] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderInspector.RefreshUI () [0x0038d] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderInspector.SelectionChanged () [0x001b1] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderSelection.NotifyOfSelectionChange (Unity.UI.Builder.IBuilderSelectionNotifier source) [0x00068] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderSelection.Select (Unity.UI.Builder.IBuilderSelectionNotifier source, UnityEngine.UIElements.VisualElement ve) [0x00088] in <0b41136f58854a5aafa95804e773dfb7>:0
at Unity.UI.Builder.BuilderViewport.OnPick (UnityEngine.UIElements.MouseDownEvent evt) [0x00063] in <0b41136f58854a5aafa95804e773dfb7>:0
at UnityEngine.UIElements.EventCallbackFunctor`1[TEventType].Invoke (UnityEngine.UIElements.EventBase evt) [0x00010] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventCallbackRegistry+DynamicCallbackList.Invoke (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target) [0x0008f] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventDispatchUtilities.HandleEventAcrossPropagationPathWithCompatibilityEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.EventBase compatibilityEvt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.VisualElement target, System.Boolean isCapturingTarget) [0x002ed] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventDispatchUtilities.DispatchToCachedElementUnderPointerOrPanelRoot (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) [0x00037] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventDispatchUtilities.DispatchToCapturingElementOrElementUnderPointer (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, System.Int32 pointerId, UnityEngine.Vector2 position) [0x0001a] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.PointerEventBase`1[T].Dispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) [0x00014] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventDispatcher.ProcessEvent (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel) [0x00039] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.EventDispatcher.Dispatch (UnityEngine.UIElements.EventBase evt, UnityEngine.UIElements.BaseVisualElementPanel panel, UnityEngine.UIElements.DispatchMode dispatchMode) [0x00046] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.BaseVisualElementPanel.SendEvent (UnityEngine.UIElements.EventBase e, UnityEngine.UIElements.DispatchMode dispatchMode) [0x0001f] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) [0x00136] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) [0x0003d] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) [0x0001a] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) [0x00001] in <bab63c62b92b4842b57501a32421fc7d>:0
at UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) [0x00079] in <baaad0161ae2487a9a523a80fa313b8d>:0