LinuxQuestions.org - XFCE screen lock fails to login after failed login attempt

I have a relatively fresh install of Debian stretch. I am using XFCE and lightdm for session management. I seem to be having a rather strange issue however. Occasionally when attempting to sign in from a lock screen, login fails stating login failure, and subsequent attempts all fail to login with no message. There is no limit on the number of times you can reattempt. No amount allows a successful login.

Observations:
1. This only appears to happen when the session has been locked.
2. It does not happen all the time.
3. It appears that the culprit could be a failed sign in attempt with a bad password (hard to verify as you can't see what you typed)
4. Switching to another vtty allows login just fine.
5. Switching back to vtty7 shows a black screen with the message "Session Locked". This message dissapears after a few seconds and you are back at the login screen.
6. Failures after this step cause a repeat of the issue.
6. Logging in with any other account, then back out, then back into the account with a locked session allows login.

I suspect the issue has something to do with lightdm or one of its modules. Just not sure what one.

/var/log/auth.log contains entries like this near these failed attempts to sign in. However, there is no indication of an authentication error prior to them.

Code:

Oct 30 12:23:05 netitechwks lightdm: pam_unix(lightdm:auth): check pass; user unknown

Oct 30 12:23:05 netitechwks lightdm: pam_unix(lightdm:auth): authentication failure; logname= uid=0 euid=0 tty=:1 ruser= rhost=

These seem to indicate to me that somehow lightdm is not pulling the username field from the login prompt? But entering a different username allows normal login.

If needed I can upload other sections of relevant logs. Any ideas are greatly appreciated.