Howdy. We installed MediaWiki 1.37.1 a few weeks back. Today we enabled this extension and noticed that all of the reference numbers are given as solely an ampersand (&). The same character for every reference number.
The output of both <references /> and {{reflist}} behave normally. The anchors seems to be functioning, as is the text-decoration that fire after clicking one of the up arrows.
Can't find anything on Google remotely related and I went through every page I could find here, plus 30 minutes looking through Phabricator without finding anything similar.
Here's a test page on my sandbox at that wiki with nothing else on it.