A logstash query for MWMultiVersion AND wiki.php suggests the first error came in on may 3rd at 15:01

Server Admin Log shows a multiversion patch deployed around an hour prior to that, seems reasonable to infer it was broken there.

https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/1141516

I ran across this today and came to phab to report it. Looks like you're way ahead of me. Thanks for the patch.

cc @Krinkle, this sounds related to your recent file reorganisation in wmf-config.

In T393415#10794050, @Pppery wrote:

https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/1141516

Yep, that's the fix. Deployed meanwhile.

@Krinkle wrote on Gerrit:

noc: Fix "Class MWMultiVersion not found" in wiki.php

In wiki.php, there is call to MWMultiVersion, but the class file
was not included.

Follows-up I808e8bb0a2d6, which removed an (indirect) include of
MWMultiVersion.php from MWConfigCacheGenerator.php, which was
accidentally masking the fact that wiki.php did not import its own
dependency.