As knc1 said, full firmware updates, meaning the password gets reset along with the rest

. Also, the root account is now locked, so you need a recent enough version of USBNetwork to work around that if you're using OpenSSH instead of dropbear.
(And as a FYI, USBNetwork hasn't ever supported the 'set a password via ;un' trick Yifan relied on for simple_usbnet, because it isn't needed with the default settings (ie. ssh over wifi disabled), like knc1 said, it doesn't check credentials over USB).
Might be a good time to switch to pubkeys and enjoy truly passwordless logins