Время от времени, в интеграционных тестах возникает вот такое исключение:

An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll

Additional information: Collection was modified; enumeration operation may not execute.

> mscorlib.dll!System.Runtime.CompilerServices.AsyncMethodBuilderCore.ThrowAsync.AnonymousMethod__6_1(object state) Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) Unknown
mscorlib.dll!System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() Unknown
mscorlib.dll!System.Threading.ThreadPoolWorkQueue.Dispatch() Unknown
[Native to Managed Transition]

Похоже, баг где-то во внутренностях фреймворка?