New version update has killed my site
I cant login to wordpress after doing the latest plugin update
There is no any change in this update which can lead to the login issue. This is not an update issue, for sure. The update process forces clearing of system cache, and you see an old issues.
Also, this can be a result of some hard code or customization you've made with wpForo files. Please make sure you don't have any custom code related to wpForo.
Leave you forum URL so we could check it.
Check all error.log files in website root directory and in /wp-admin/ folder via FTP. Make sure there are not errors in Forums > Tools > Debug Tab