Keeps getting logged out

If you cannot stay logged in on wpsecurityninja.com/account/, open Freemius directly:

https://users.freemius.com/

Also try:

1. Another browser, or Chrome Incognito / Firefox Private mode
2. Disabling extensions that block cookies or third-party storage
3. Clearing cookies for wpsecurityninja.com and freemius.com, then signing in again

Related: Problems logging in, First time logging in.