I turned off auto login and tried to log into my maintenance account to update something unrelated, last used installing the .114 web driver apparently. Result, blank screen and kicked back to login window after a few seconds. Could speculate that auto login creates a constant blank screen while the login retries/fails. Logged into my regular account and found removing ~/Library/ByHost/com.apple.windowserver* for the problem account resolved the issue and i was able to login. Working .121 web drivers were incompatible with the previous version of that file. The last 'blast from the past' concerning the web drivers on 10.13 on this machine i hope.