What happens when you do the same test on the CIFS host machine? How far apart are the .NET Core app and CIFS server? It's not clear from your question whether they're both in Azure, or if they're in different data centers. If the two machines aren't side-by-side in the same data center rack, then I'd try to find a way to disable UDP, if that's possible with CIFS. I tried some web searches, but didn't come up with a method to get TCP-only CIFS.