Commons has Tabular data namespace (namespace number 486). Cat-a-Lot shows up on the pages in that namespace; however adding any category results in "The content format text/x-wiki is not supported by the content model Tabular.JsonConfig. " error. We should disable Cat-a-Lot in that namespace.
Guess this would require edits to https://commons.wikimedia.org/wiki/MediaWiki:Gadget-Cat-a-lot.js . Looks like the namespace number for JsonConfig is 486 as per https://noc.wikimedia.org/conf/CommonSettings.php.txt and https://www.mediawiki.org/wiki/Extension_default_namespaces
I'd advocate disabling things like this, based on wgPageContentModel. While namespaces have a default contentmodel, that doesn't mean mean that namespaces always have their default content model.
Regardless, this seems like a local wiki problem, the gadget is not part of the official software and will have to be fixed by technical users of the Commons community.