It looks like the Commons link constraint type doesn’t support the Creator namespace. Example statement: https://www.wikidata.org/wiki/Q468214#P1472, with the value “Ludolf Bakhuizen” and the namespace “Creator” on the constraint. I suspect this might be because we use a TitleParser configured on wikidatawiki, where there’s no Creator namespace. But perhaps it works if we have the TitleParser parse commons:Creator:Ludolf Bakhuizen instead of just Creator:Ludolf Bakhuizen?
But perhaps it works if we have the TitleParser parse commons:Creator:Ludolf Bakhuizen…?
Nope. The way the MediaWiki config for Wikimedia’s sites is set up, wikidatawiki just doesn’t know anything about commonswiki’s namespaces (or any other site-specific config). I’m afraid we’ll just have to hardcode this. (It’s not like CommonsLinkChecker is particularly suited for other wikis anyways right now… if we ever get around to T169538: Make “Commons link” constraint configurable, then we can also make the extra namespaces configurable, but for now, hardcoding will do.)