A legitimate interest consent is only valid for a limited amount of time. After that, the consents are ignored, and contacts won't be included in your marketing communication unless they have another consent to the same subscription type, which is still valid.
The validity of a legitimate interest consent depends on various factors. It's important to seek advice from your legal advisor to determine if, and for how long, you can rely on legitimate interest consents.
Set the validity time
Go to Settings -> Consent and scroll to the bottom of the page. Choose the preferred validation time and click on "Save changes". The settings will be active immediately.