Why segfault when trying to access a raw pointer from a unique_ptr returned by lambda?

I am trying to understand why this is not possible. Suppose I have a ctor for object Foo that accepts a lambda which returns a std::unique_ptr for an object Bar. Using capture value, I want to save the the raw pointer of the returned std::unique_ptr to a variable outside the lambda.

Bar* bar_ptr;

auto foo = std::make_unique<Foo>([this]()
{ 
 auto bar = std::make_unique<Bar>();
 bar_ptr = bar.get();
 return bar;
})

// Assume foo is alive, has called the lambda, has ownership of bar and does not destroy it.

bar_ptr->DoSomething(); // fails

My only guess is that it is something to do with the implicit move because of return bar. However I have other code where a std::move is no issue like so:

auto bar = std::make_unique<Bar>();
Bar* bar_ptr = bar.get();
auto foo = std::make_unique<Foo>(std::move(bar));

bar_ptr->DoSomething() // no problem