I can only log into 1 password protected category at a time
You can only unlock one password protected category at a time.
If you log into one password protected category and then log into another, you will find that you have been logged out of the second category and need to re-enter the password.
This is the way that the password protection cookie works in WordPress, and comes from WordPress itself rather than our plugin. You can read more here.
We recommend that you structure your website in a way that will naturally encourage users to access one category at a time.