I tried the plugin in vBulletin 5.1.4 Beta 2 and the following error occurs:
You can not access any forum page, since all pages returned the following message on a blank page:
Critical Error
We are currently experiencing Technical Difficulties. Please check back in 24 hours.
However, if you are logged into the forum everything works fine, but when you log out or want to see any forum pages without login, this error message appears.
I hope it gets fixed