Umbraco-CMS: Images are missing and can't refresh Memory Cache

We can’t refresh our Memory Cache on a V8-website. We first saw this error on Umbraco 8.5.5 but it’s still present in 8.6.0.

The symptoms are similar to this https://github.com/umbraco/Umbraco-CMS/issues/7766 and this https://github.com/umbraco/Umbraco-CMS/issues/7756 but in our case a “Save” of the Media Item will not update the cache either.

Umbraco version

I am seeing this issue on Umbraco version: 8.6, and also when we where running on 8.5.5. The site has been upgrade from at least 8.4 before.

Specifics

We had issues on Umbraco 8.5.5 that the cache suddenly would not update, when triggering a Refresh (from the Settings-section Dashboard) we got an error message.

Since 8.6 was released today we figured an upgrade maybe could solve this, but after the upgrade the symptoms are still there.

A strange thing is that the cache is populated correctly for us after a restart, so basiclly:

1. Start the site and things works
2. Go to Backoffice / Settings and hit “Refresh Memory Cache”
3. Error message below are shown
4. Almost all media-pickers resolve to “null” on the front end
5. Restart the site by touching web.config
6. All images works again on the front end.
7. Try step 2 again and we’ll get the same error.

Error message:

An error occured
Object reference not set to an instance of an object.

Exception Details
System.NullReferenceException: Object reference not set to an instance of an object.

at Umbraco.Web.PublishedCache.NuCache.ContentStore.AddTreeNodeLocked(ContentNode content, LinkedNode`1 parentLink) in D:\a\1\s\src\Umbraco.Web\PublishedCache\NuCache\ContentStore.cs:line 1031
   at Umbraco.Web.PublishedCache.NuCache.ContentStore.SetAllLocked(IEnumerable`1 kits) in D:\a\1\s\src\Umbraco.Web\PublishedCache\NuCache\ContentStore.cs:line 762
   at Umbraco.Web.PublishedCache.NuCache.PublishedSnapshotService.LoadMediaFromDatabaseLocked(IScope scope, Boolean onStartup) in D:\a\1\s\src\Umbraco.Web\PublishedCache\NuCache\PublishedSnapshotService.cs:line 470
   at Umbraco.Web.PublishedCache.NuCache.PublishedSnapshotService.NotifyLocked(IEnumerable`1 payloads, Boolean& anythingChanged) in D:\a\1\s\src\Umbraco.Web\PublishedCache\NuCache\PublishedSnapshotService.cs:line 792
   at Umbraco.Web.PublishedCache.NuCache.PublishedSnapshotService.Notify(JsonPayload[] payloads, Boolean& anythingChanged) in D:\a\1\s\src\Umbraco.Web\PublishedCache\NuCache\PublishedSnapshotService.cs:line 768
   at Umbraco.Web.Cache.MediaCacheRefresher.Refresh(JsonPayload[] payloads) in D:\a\1\s\src\Umbraco.Web\Cache\MediaCacheRefresher.cs:line 46
   at Umbraco.Core.Sync.ServerMessengerBase.Deliver[TPayload](ICacheRefresher refresher, TPayload[] payload) in D:\a\1\s\src\Umbraco.Core\Sync\ServerMessengerBase.cs:line 295
   at Umbraco.Web.Cache.DistributedCache.RefreshByPayload[TPayload](Guid refresherGuid, TPayload[] payload) in D:\a\1\s\src\Umbraco.Web\Cache\DistributedCache.cs:line 83
   at Umbraco.Web.Cache.DistributedCacheExtensions.RefreshAllMediaCache(DistributedCache dc) in D:\a\1\s\src\Umbraco.Web\Cache\DistributedCacheExtensions.cs:line 163
   at Umbraco.Web.Cache.DistributedCacheExtensions.RefreshAllPublishedSnapshot(DistributedCache dc) in D:\a\1\s\src\Umbraco.Web\Cache\DistributedCacheExtensions.cs:line 184
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass6_1.<GetExecutor>b__0(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__15.MoveNext()

Expected result

For the cache to refresh