And fixed. Wiki appears to be nominally operational again.
And, what was it? Some functionality used by dokuwiki via PHP had shifted packages with change in PHP version (and Debian major version ... but had only more recently changed Apache to use the newer PHP version). Was easy enough to find when searching on the specific error messages seen in the Apache logs, along with dokuwiki.
From: "Michael Paoli" Michael.Paoli@cal.berkeley.edu Subject: Wiki "temporarily" (mostly) down Date: Wed, 28 Aug 2019 06:41:24 -0700
The BALUG Wiki is "temporarily" (mostly) down for a bit. I'm integrating WordPress (not for BALUG, but for BerkeleyLUG) on same host & server ... that required web server to use newer php version to work with WordPress ... which has "temporarily" (mostly) broken the BALUG Wiki. Index pages themselves still appear to work, e.g.: https://www.wiki.balug.org/wiki/doku.php?do=index&idx=balug but contents pages, e.g.: https://www.wiki.balug.org/wiki/doku.php?id=balug:cds_and_images_etc presently fail.
I'm hoping/presuming it's just some config bit(s) I need to track down and correct/adjust, then all should be fine again.