I've had a heck of a time convincing our host that the problem with PCIM being down was on their end. They promised they would look into it in tech support. Guess they found the problem on their end after all.
The site had been upgraded to PHP 7.4, which the installed version of XenForo is not friends with. Don't give the host too much credit though -- they didn't fix it.
It's a non-issue as long as we stay on 7.2, but it's also an issue in that we can't upgrade to any newer version until XenForo is upgraded, as those deprecations, starting with PHP 7.3, turn into removals (i.e. no more compatibility code). Staying on 7.2 is also an issue as it's (beyond) EOL.