Consider the following code:

var dst = bucket.OpenUploadStream(srcFile.Name);
srcFile.OpenRead().CopyTo(dst);
// dst.Close(); // Correctly writes fs.files collection
((Stream)dst).Close(); // Does NOT write to fs.files collection{{}}

Looks like it's missing Close() override for NETSTANDARD2_0 that'll close the wrapped stream?  GridFSUploadStreamCompat.cs Line 80

This leads to some pretty difficult to diagnose issues when the stream is used in any number of generic libraries that works against the Stream interface.