Manual:$wgUpdateCompatibleMetadata/en

Details
Whether to automatically update the $metadata field in the database, if the metadata becomes outdated (say, after a major upgrade of MediaWiki) but can be automatically updated to the current format. This update would take place when viewing the image page, or alternatively, it could be forced by running the $refreshImageMetadata maintenance script.

This setting defaults to false, because during a code update, a lot of images could suddenly have outdated metadata. Regenerating all of them could overload the server if it is a busy server.