On some servers if you adds multiple slashes at the end of the URL, the server will handle the request wrong. If a bot visits https://www.yoursite.com/wp-json/wp/v2/users///// it will cache the rest response but the request URI will be dropped by the server and the cache will be generated for the homepage.

To avoid it, please go to Swift Performance Settings, open Caching » Tweaks tab and enable Strict Host. Then please clear all cache via FTP (delete wp-content/cache/swift-performance folder), it will solve the issue.