Hi Team,

I've used Episerver 9.x and everthing worked fine. After the upgrade to the Episerver 10.1 I'm expririencing strange behaveiour for some pages. 
Exception: "Failed to Get because of circular references" occurs, but not every time. It seems that issue occurs while loading blocks.

This is the stacktrace:

Failed to Get because of circular references

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

[InvalidOperationException: Failed to Get because of circular references]
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.ValidateCircularReference(ContentReference contentLink, HashSet`1 visitedContents) +456
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink, HashSet`1 visitedContents) +97
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.GetSetting(ContentReference contentLink, HashSet`1 visitedContents) +263
   System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) +84
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.GetSetting(ContentReference contentLink, HashSet`1 visitedContents) +263
   System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) +84
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.GetSetting(ContentReference contentLink, HashSet`1 visitedContents) +263
   System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) +84
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink) +12
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink, String languageBranch) +18
   EPiServer.Core.Internal.LanguagePipeline.Pipe(ContentReference contentLink, IContent contentInstance, LoaderOptions loaderOptions, Func`3 loadingDelegate) +278
   EPiServer.Core.Internal.ProviderPipelineImplementation.GetItem(ContentProvider provider, ContentReference contentLink, LoaderOptions loaderOptions) +489
   EPiServer.Core.Internal.DefaultContentLoader.TryGet(ContentReference contentLink, LoaderOptions loaderOptions, T& content) +589
   EPiServer.Core.Html.StringParsing.ContentFragment.GetContent(Boolean enableMasterLanguageFallback) +206
   EPiServer.Core.Html.StringParsing.ContentFragment.GetSecurityDescriptor() +33
   EPiServer.Core.Html.StringParsing.StringFragmentCollection.AddFilteredFragment(String contentGroup, List`1 filteredFragments, IStringFragment fragment, ISecurable securable, IPrincipal principal) +37
   EPiServer.Core.Html.StringParsing.StringFragmentCollection.GetFilteredFragments(IPrincipal principal) +450
   EPiServer.Core.ContentArea.get_FilteredItems() +55
   EPiServer.Web.Mvc.Html.ContentAreaRenderer.Render(HtmlHelper htmlHelper, ContentArea contentArea) +320
   ASP.util_views_shared_displaytemplates_contentarea_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in E:\work\Test\Project\Source11\Episerver\ProjectGroup.Web\Util\Views\Shared\DisplayTemplates\ContentArea.ascx:4
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +263
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +80
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +160
   System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +76
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +80
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +8921

The same error occurs in the CMS (after reloading page - every time), but it is visible in Chrome/Network tab, where the stacktrace is a bit differrent:

http://mywebsite.local/EPiServer/cms/Stores/contentstructure/726?dojo.preventCache=1481210450729

[InvalidOperationException: Failed to Get because of circular references]
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.ValidateCircularReference(ContentReference contentLink, HashSet`1 visitedContents) +456
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink, HashSet`1 visitedContents) +97
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.GetSetting(ContentReference contentLink, HashSet`1 visitedContents) +263
   System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) +84
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.GetSetting(ContentReference contentLink, HashSet`1 visitedContents) +263
   System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) +84
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink) +12
   EPiServer.Core.Internal.DefaultContentLanguageSettingsHandler.Get(ContentReference contentLink, String languageBranch) +18
   EPiServer.Core.Internal.LanguagePipeline.Pipe(ContentReference contentLink, IContent contentInstance, LoaderOptions loaderOptions, Func`3 loadingDelegate) +278
   EPiServer.Core.Internal.ProviderPipelineImplementation.GetItem(ContentProvider provider, ContentReference contentLink, LoaderOptions loaderOptions) +489
   EPiServer.Core.Internal.DefaultContentLoader.TryGet(ContentReference contentLink, LoaderOptions loaderOptions, T& content) +589
   EPiServer.Cms.Shell.UI.Rest.Internal.ContentStructureStore.GetContent(ContentReference contentReference, DefaultQueryParameters queryParameters) +85
   EPiServer.Cms.Shell.UI.Rest.Internal.ContentStructureStore.Get(ContentReference id, String query, ContentReference referenceId, String[] typeIdentifiers, Nullable`1 allLanguages, IEnumerable`1 sortColumns, ItemRange range) +372
   lambda_method(Closure , ControllerBase , Object[] ) +437
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +229
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +35
   System.Web.Mvc.Async.AsyncControllerActionInvoker.b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState) +39
   System.Web.Mvc.Async.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +42
   System.Web.Mvc.Async.AsyncInvocationWithFilters.b__3d() +72
   System.Web.Mvc.Async.<>c__DisplayClass46.b__3f() +386
   System.Web.Mvc.Async.<>c__DisplayClass46.b__3f() +386
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +42
   System.Web.Mvc.Async.<>c__DisplayClass2b.b__1c() +38
   System.Web.Mvc.Async.<>c__DisplayClass21.b__1e(IAsyncResult asyncResult) +186
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +38
   EPiServer.Shell.Services.Rest.RestControllerBase.EndExecute(IAsyncResult asyncResult) +60
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +399
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +137

I've found related question here: http://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2016/11/what-does-this-error-message-in-editor-mode-mean/

Is this known issue with the Episerver 10.1?  Coluld you please advise?

Regards,

Milos