roslyn: TryGetTagIntervalTreeForBuffer InvalidOperationException on Startup

Version Used: Version 16.5.0 Preview 3.0 [29715.144.master]

Steps to Reproduce:

1. Open Compilers.sln or Roslyn.sln

Expected Behavior:

No exceptions.

Actual Behavior:

System.InvalidOperationException: Unexpected false
   at Roslyn.Utilities.Contract.ThrowIfFalse(Boolean condition, String message)
   at Microsoft.CodeAnalysis.Editor.Shared.Utilities.ForegroundThreadAffinitizedObject.AssertIsForeground()
   at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.TagSource.TryGetTagIntervalTreeForBuffer(ITextBuffer buffer)
   at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.Tagger.GetTagsWorker(NormalizedSnapshotSpanCollection requestedSpans, Boolean accurate, CancellationToken cancellationToken)
   at Microsoft.CodeAnalysis.Editor.Tagging.AbstractAsynchronousTaggerProvider`1.Tagger.GetTags(NormalizedSnapshotSpanCollection requestedSpans)
   at Microsoft.VisualStudio.Text.Tagging.Implementation.TagAggregator`1.<GetTagsForBuffer>d__47.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)

Dump saved at: \\mlangfs1\public\frsilb\dumps\41009\devenv.dmp