Most people won’t spend long enough on a discussion page without doing anything else to trigger this.
It’s designed to prevent cross-site request forgery (CSRF) attacks where another site sends a request to the community to perform an action on your behalf.
Any action requires a valid CSRF token to perform an action, and this token is linked to your forum session in the background.
There’s no way to disable this and there’s no reason anyone ever should.
It’s so that, if your CSRF token was stolen, it would only work for 20 mins or so. 20 mins of damage is better than 2 hours or a day. There shouldn’t be any way for the CSRF to be stolen, but things happen.
This is not designed to protect your account from people logging in as you or accessing the forum as you – purely to prevent other sites from attempting to perform actions as you.