Can you tell where the problem is?
So part of the problem is that there is a lot that I don't know about your environment/requirements.
If you are using WinFSP and SSHFS-win to map that psuedo network "Z" drive, then it's not a "normal" network drive to a Windows SMB file share. Functionality is going to be limited. (See my first comment.) Is there a reason that you are using that software?
An educated guess is that you have that drive definition configured to be read-only.
If WinSCP works correctly (SFTP/SSH client <<--->> SSH server), then why don't you just use that software? That would lead me to believe that your problems are related to your use of WinFSP and SSHFS-win. If they don't work correctly, then you would need to ask for help in their support forums. They do not appear to be Microsoft software.
If your client and server machines are on the same private network, then why don't you use a good old mapped drive to a network share on the Win10 "server"? That would allow you to use the Windows explorer as a client without using any 3rd party tools. And if you needed to access the server folder via SFTP on an Android device, you could still have OpenSSH point to the same folder that is shared out.