Security expert Alec Muffett discovered that the messages once disappeared can still be recovered from the recipients device. The disappearing messages in Signal are automatically deleted after a specific interval of time set up by the sender. Signal, does not explicitly delete this notification when it deletes messages from the app UI. Security expert Patrick Wardle analyzed the issue and found that the disappearing messages are stored in a user-readable database of the OSThe message may still remain in the. Notification Center, which contains the message contents, is recorded by the OS.”]
Source: https://securityaffairs.co/wordpress/72315/security/signal-disappearing-messages.html