It appears that the pluginPlugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party checksum download endpoint has had some rate limiting added, which is affecting clients of that endpoint.
The legitimate uses of the endpoint do result in the checksums of all plugins on a site being requested in a short period of time. I’m unsure if clients avoid requesting 404 urls or only 200’s.