ssh to server works, but sshfs gives permission error

Reproduce the net use p: \\sshfs\root@target2 and \\sshfs.k commands against the Dropbear 2020.80 target, comparing them with the working Ubuntu target. Start by examining the reported authentication and system error codes and any available sshfs-win or Dropbear logs. Done means identifying the compatibility or configuration cause and documenting a confirmed diagnosis or fix.

Summary

• ssh and sshfs-win work for Target1 (Ubuntu16.04)
• ssh works for Target2 (custom embedded Linux) but sshfs-win does not work and gives permission error

Details

I understand that sshfs-win does not use the native windows OpenSSH, which might be why, for target2, I can ssh (with OpenSSH) but I cannot sshfs-win.

I will still provide the full version information here, in case it's helpful to diagnose my problem:

Host: Windows 10

C:\windows\system32>where ssh
C:\Windows\System32\OpenSSH\ssh.exe

C:\windows\system32>ssh -V
OpenSSH_for_Windows_8.1p1, LibreSSL 3.0.2

C:\windows\system32>

Target1: Ubuntu16.04

This Linux is running inside VirtualBox and is a standard Ubuntu16.04 distribution, running sshd

sshd -v
unknown option -- v
OpenSSH_7.2p2 Ubuntu-4ubuntu2.10, OpenSSL 1.0.2g  1 Mar 2016

• ssh works and sshfs-win works, both with password authentication and private/public key authentication

Target2: Custom Linux distro

This is a custom built Linux distro running on an ARM embedded platform. It is running Dropbear SSH as the SSH daemon:

# dropbear -v
Invalid option -v
Dropbear server v2020.80 

https://matt.ucc.asn.au/dropbear/dropbear.html

I can ssh to this target2 both with password and private/public key authentication.
However, when I run:

net use p: \\sshfs\root@target2

I get:

C:\windows\system32>net use p: \\sshfs\root@target2
The password is invalid for \\sshfs\root@target2.

Enter the user name for 'sshfs': root
Enter the password for sshfs:
System error 5 has occurred.

Access is denied.


C:\windows\system32>

and when I try \\sshfs.k to specify private/public key authentication, I get:

C:\windows\system32>net use p: \\sshfs.k\root@target2
System error 67 has occurred.

The network name cannot be found.


C:\windows\system32>

Any help on how to diagnose this, how to enable debugging, how to look at logs would be greatly appreciated!