LanguageSettingsPersister.TryFetch assertion is being hit

[davkean]

Version Used:
16.6.0 Preview 2

Steps to Reproduce:

No repro. This is being hit in our fault telemetry and is new for 16.6.

["Roslyn.Utilities.Contract.Fail(String) Unexpected true
>>>Roslyn.Utilities.Contract.ThrowIfTrue(Boolean)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.Options.LanguageSettingsPersister.TryFetch(OptionKey,Object&)
>>>Microsoft.CodeAnalysis.Options.GlobalOptionService.LoadOptionFromSerializerOrGetDefault(OptionKey)
>>>Microsoft.CodeAnalysis.Options.GlobalOptionService.GetOption_NoLock(OptionKey)
>>>Microsoft.CodeAnalysis.Options.GlobalOptionService.GetSerializableOptionValues(ImmutableHashSet`1,ImmutableHashSet`1)
>>>Microsoft.CodeAnalysis.Options.GlobalOptionService.GetSerializableOptionsSnapshot(ImmutableHashSet`1,IOptionService)
>>>Microsoft.CodeAnalysis.Options.OptionServiceFactory.OptionService.GetSerializableOptionsSnapshot(ImmutableHashSet`1)
>>>Microsoft.CodeAnalysis.Options.SerializableOptionSet.WithLanguages(ImmutableHashSet`1)
>>>Microsoft.CodeAnalysis.SolutionState.Branch(SolutionAttributes,IReadOnlyList`1,SerializableOptionSet,ImmutableDictionary`2,ImmutableDictionary`2,ImmutableDictionary`2,ProjectDependencyGraph)
>>>Microsoft.CodeAnalysis.SolutionState.AddProject(ProjectId,ProjectState)
>>>Microsoft.CodeAnalysis.SolutionState.AddProject(ProjectInfo)
>>>Microsoft.CodeAnalysis.Solution.AddProject(ProjectInfo)
>>>Microsoft.CodeAnalysis.Workspace.OnProjectAdded_NoLock(ProjectInfo,Boolean)
>>>Microsoft.CodeAnalysis.Workspace.OnProjectAdded(ProjectInfo,Boolean)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioProjectFactory.<>c__DisplayClass5_0.<CreateAndAddToWorkspace>b__0(Workspace)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioWorkspaceImpl.ApplyChangeToWorkspace(Action`1)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioProjectFactory.CreateAndAddToWorkspace(String,String,VisualStudioProjectCreationInfo)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.CPS.CPSProjectFactory.CreateVisualStudioProject(String,String,String,IVsHierarchy,Guid)
>>>Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.CPS.CPSProjectFactory.Microsoft.VisualStudio.LanguageServices.ProjectSystem.IWorkspaceProjectContextFactory.CreateProjectContext(String,String,String,Guid,Object,String)
>>>Microsoft.VisualStudio.ProjectSystem.LanguageServices.WorkspaceProjectContextProvider.<CreateProjectContextHandlingFaultAsync>d__8.MoveNext()
>>>System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
>>>Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception)
>>>Microsoft.VisualStudio.ProjectSystem.ProjectErrorReporting.<>c__DisplayClass6_0.<SubmitErrorReport>b__0()
>>>Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.<Guard>g__action|0()
>>>GuardMethodClass.GuardMethod(Func`1,Func`2,Func`2)"]

[tmat]

This is not just debug assertion, it's causing gold bar:

=====================
7/15/2021 11:50:41 AM
LimitedFunctionality
System.InvalidOperationException: Unexpected true - line 232
   at Roslyn.Utilities.Contract.Fail(String message, Int32 lineNumber)
   at Roslyn.Utilities.Contract.ThrowIfTrue(Boolean condition, Int32 lineNumber)
   at Microsoft.VisualStudio.LanguageServices.Implementation.Options.LanguageSettingsPersister.TryFetch(OptionKey optionKey, Object& value)
   at Microsoft.CodeAnalysis.Options.GlobalOptionService.LoadOptionFromSerializerOrGetDefault(OptionKey optionKey)
   at Microsoft.CodeAnalysis.Options.GlobalOptionService.GetOption_NoLock(OptionKey optionKey)
   at Microsoft.CodeAnalysis.Options.GlobalOptionService.GetSerializableOptionValues(ImmutableHashSet`1 optionKeys, ImmutableHashSet`1 languages)
   at Microsoft.CodeAnalysis.Options.GlobalOptionService.GetSerializableOptionsSnapshot(ImmutableHashSet`1 languages, IOptionService optionService)
   at Microsoft.CodeAnalysis.Workspace.CreateSolution(SolutionInfo solutionInfo)
   at Microsoft.CodeAnalysis.Workspace.OnSolutionAdded(SolutionInfo solutionInfo)
   at Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioProjectFactory.<>c__DisplayClass9_0.<CreateAndAddToWorkspaceAsync>b__0(Workspace w)
   at Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioWorkspaceImpl.ApplyChangeToWorkspace(Action`1 action)
   at Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.VisualStudioProjectFactory.<CreateAndAddToWorkspaceAsync>d__9.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 Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.CPS.CPSProjectFactory.<CreateProjectContextAsync>d__8.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 Microsoft.VisualStudio.Threading.JoinableTask.CompleteOnCurrentThread()
   at Microsoft.VisualStudio.Threading.JoinableTask`1.CompleteOnCurrentThread()
   at Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem.CPS.CPSProjectFactory.Microsoft.VisualStudio.LanguageServices.ProjectSystem.IWorkspaceProjectContextFactory.CreateProjectContext(String languageName, String projectUniqueName, String projectFilePath, Guid projectGuid, Object hierarchy, String binOutputPath, String assemblyName)
   at Microsoft.VisualStudio.ProjectSystem.LanguageServices.WorkspaceProjectContextProvider.<CreateProjectContextHandlingFaultAsync>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.VisualStudio.ProjectSystem.CommonProjectSystemTools.Rethrow(Exception ex)
   at Microsoft.VisualStudio.ProjectSystem.ExceptionFilter.<>c__DisplayClass2_0.<Guard>g__Action|0()
   at GuardMethodClass.GuardMethod(Func`1 , Func`2 , Func`2 )
===================