They shouldn’t be reverting upgrades, especially something as critical as php. Regular updates are normal part of managing any software, and it should be done frequently. Security fixes, performance improvements, bug fixes, are all important reasons to keep upgrading software. Otherwise you’ll end up accumulating technical debt, and best case scenario is blue, unreadable forum, worst case, someone compromises the server, and do lots of nasty things. They should update vBulletin to the most recent version and then fix appearance, or move forum software to something more modern, like NodeBB or Discourse, using vBulletin in 2020 is like using Windows XP. Will it work, sure, but it’s archaic, obsolete and there are free and modern alternatives.