Occurring in production.
Can be replicated at this URL:
https://login.wikimedia.org/wiki/Special:Log/block?page=User:Majavah&useskinversion=2&useskin=vector
Impact:
14 exceptions in last hour, seems to only impact login wiki logged in users
Loginwiki offline for Vector: https://login.wikimedia.org/wiki/Main_Page VS https://login.wikimedia.org/wiki/Main_Page?useskin=minerva