When an unmatched literal square bracket is used in the title of a reference, Parsoid or VisualEditor encloses it in a nowiki tag.
Example on the live wiki: https://en.wikipedia.org/w/index.php?title=Wikipedia&diff=566045928&oldid=566042453#cite_ref-209 (line 360)
Examples in testing: https://en.wikipedia.org/w/index.php?title=User%3AThryduulf%2Fsandbox&diff=566402676&oldid=566401436
It is possible this is a reappearance of or related to T45067
Version: unspecified
Severity: normal
See Also:
T45067: Parsoid: Square brackets sometimes (but not always) get escaped with <nowiki>s when PHP parser wouldn't
T52331: VisualEditor throws <nowiki> next to any square bracket [