Second one was, IIRC, one of the primary motivating use cases for IAsyncEnumerable<T>. It has to be IAsyncEnumerable<T> all the way up and down, but it's elegant enough. Quite often, depending on the API, it might naturally be implemented by a variant of "paging" behind the scenes. One advantage here is that since the updates throughout the final await foreach can happen entirely on the UI thread (assuming a compliant SynchronizationContext.Current, which is the case at least for WPF), you can see the results streaming in one-by-one as they arrive from the original repository if you want.

Before watching the video, from the title, I correctly guessed what the first bug would be, but my guess for what bug #2 would be was one that's more related to the far more insidious one that he describes starting at 17:27. You don't have to get very fancy to see connections held open too long:

I don't know how common it is more broadly, but I've seen plenty of code that overlooks using and just directly calls Dispose (or, more commonly, a Close method). While it's generally advised to favor using over directly calling Dispose, admittedly it's not always a huge deal: if you don't otherwise have a robust story for what happens when exceptions get thrown, then it doesn't ordinarily matter that you're not explicitly cleaning up those resources, since the program might just be ending anyway.

With iterators, this can leave the connection open even if no exception is thrown. try/finally blocks (including using scopes, which I assume still get lowered to the same) get extra treatment to make sure that the finally part gets executed when the iterator is disposed, which happens at the end of any foreach loop over it (including the implicit loop behind calls like .First).