public class MyBlockValidator : IValidate<MyBlock>
	{
		public IEnumerable<ValidationError> Validate(MyBlock instance)
		{
			if (instance.ImageContainer?.Image != null && (!string.IsNullOrEmpty(instance.VideoUrl) || instance.Screen9Video != null))
			{
				yield return new ValidationError
				{
					ErrorMessage = LocalizationService.Current.GetString(Global.LocalizationStringKeys.Validation.VideoAndImageNotAllowed),
					Severity = ValidationErrorSeverity.Error,
					ValidationType = ValidationErrorType.Unspecified,
					PropertyName = nameof(MyBlock.ImageContainer),
					RelatedProperties = new[] { nameof(MyBlock.VideoUrl), nameof(MyBlock.Screen9Video) }
				};
			}

			if ((instance.Screen9Video != null || !string.IsNullOrEmpty(instance.VideoUrl)) && string.IsNullOrWhiteSpace(instance.VideoTitle))
			{
				yield return new ValidationError
				{
					ErrorMessage = LocalizationService.Current.GetString(Global.LocalizationStringKeys.Validation.VideoTitleMissing),
					Severity = ValidationErrorSeverity.Error,
					ValidationType = ValidationErrorType.Unspecified,
					PropertyName = nameof(MyBlock.VideoTitle),
					RelatedProperties = new[] { nameof(MyBlock.VideoUrl), nameof(MyBlock.Screen9Video) }
				};
			}

			yield break;
		}
	}

Having implemented validation on a block works when editing an existing block but breaks on new block

Dojo gets status 409 "The page was not displayed because there was a conflict"

Any ideas on why?