Linux – Windows 10 Password Error with Samba Share

I am trying to connect to a samba share with Windows 10 Pro (Version 1511, Build 10586.589) using the command net use L: \\myserver\myshare /u:myuser mypassword. I get the error:

System error 86 - The specified network password is not correct.

I get the same result when using the Map network drive dialog.
Other clients (Android, Linux) can connect just fine with the same user/password.

I have tried adjusting the following security policies via secpol.msc:

• Microsoft network client: Send unencrypted password to third-party
  SMB servers (enabled and disabled)
• Netword security: LAN Manager authentication level (Send LM & NTLM responses, Send LM & NTLM – use NTLMv2 session security if negotiated
• Network security: Minimum session security for NTLM SSP based
  clients/servers (128-bit encryption and none)

I am running samba 4.5.0-2 on Arch Linux (4.7.4-1). Server-side, I have reset the user password, removed and re-added the user to the smbpasswd backend, and started and restarted the smbservice.

My smbconf is basically the default:

 [global]
   workgroup = MYGROUP
   server string = Samba Server
   log file = /var/log/samba/%m.log
   max log size = 50
   security = user
   encrypt passwords = yes
   smb passwd file = /etc/samba/smbpasswd
   unix password sync = Yes
   passwd program = /usr/bin/passwd %u
   passwd chat = *New*UNIX*password* %n\n *ReType*new*UNIX*password* %n\n *passwd:*all*authentication*tokens*updated*successfully*
   dns proxy = no
[my share]
   comment = my share
   browseable = yes
   writable = yes
   guest ok = no
   path = /pathto/myshare
   public = no
   valid users = myuser
   create mask = 770

I don't see anything out of the ordinary in testparm, and I have confirmed via pdbedit that my user is definitely registered with the backend.

It has worked fine before today and I do not know why it suddenly stopped working. Any advice is greatly appreciated.