A small change has been made to $wgCanonicalNamespaceNames in MediaWiki core (see https://phabricator.wikimedia.org/T232004).
This appears to change the $namespaces variable set on this line of code.
[ ... 0 => "<Main>", ... ]
[ ... 0 => "", ... ]
I don't know what impact that will have.
The change will be in 1.34.wmf.22, so I don't believe will affect you yet, but possibly in the future.