It doesn't matter.
Ubuntu Desktop is Ubuntu with some extra desktop packages.
Ubuntu Server is Ubuntu with some extra server packages.
You can add server packages to Desktop. You can add desktop packages to Server. It's all Ubuntu.
Most new users find it easiest to install Ubuntu Desktop, and add some server packages to it.
Ubuntu Desktop ...
Thank you everyone for the guidance and help. After it became apparent that it was unlikely this was a samba issue, I spent some time today searching for possible causes in Windows.
I ran across the article below, followed the solution, and both desktop computers were immediately able to access the samba share.
Article with Solution: https://superuser....
Samba is to connect different computer over the network. This situation is not applicable for you, because your partitions exist on the same computer.
What you are looking for is to have your second partition (the Windows partition) automatically mounted after startup.
By default, your Windows partition is not connected when you start Ubuntu. You can, ...
As per your Comment if you already have samba 4.10 and only observe the symptoms using the GUI, use the command line to copy files as there is a bug in Dolphin which is being addressed and whose fix will eventually make it into Nautilus as well.
(Read the bug's fix at a minimum: interesting read)
Try to add or modify the next socket option in your smb.conf file under [global] section:
socket options = IPTOS_LOWDELAY TCP_NODELAY SO_SNDBUF=64000 SO_RCVBUF=64000 SO_KEEPALIVE
Then restart samba services:
sudo systemctl restart nmbd smbd
Another option is compiling it from sources or downloading older version from 16.04 repository. But I couldn't ...