Autofac: ObjectDisposedException when resolving dependencies from factory delegate in ASP.NET Web API

I have an ASP.NET Web API project using Autofac for dependency injection.

I register a factory for creating ICommandExecutor based on an enum:

builder.Register<Func<CommandType, ICommandExecutor>>(c =>
{
    var context = c.Resolve<IComponentContext>();
    return commandType => context.ResolveNamed<ICommandExecutor>(commandType.ToString());
})
.SingleInstance();

My executors are registered as keyed singletons:

builder.RegisterType<QueryExecutor>()
       .Named<ICommandExecutor>(CommandType.Query.ToString())
       .SingleInstance();

builder.RegisterType<IngestExecutor>()
       .Named<ICommandExecutor>(CommandType.Ingest.ToString())
       .SingleInstance();

When my Web API controllers call into this factory during a request, things work most of the time.

But intermittently, calling the function throws an exception:

System.ObjectDisposedException: Instances cannot be resolved and nested lifetimes cannot be created from this LifetimeScope as it (or one of its parent scopes) has already been disposed.

This is confusing because:

• The request pipeline hasn't finished yet (so the request scope should still be alive)

• The executors themselves are registered as SingleInstance

What I tried

• Checked the Web API request scope lifetime – it's still active when this happens. As I can see logs even after this exception.

Question

• Why does this happen even though the request is still running?