When I re-visit my website, I'm not asked to re-enter the password
When you enter the correct password, a cookie is set which unlocks the category for 10 days (you can change this in the plugin settings). This means that if you revisit the category from the same web browser then you will not be asked to enter the password again.
This is intended behavior and saves your customers having to re-enter the password within a short period.
If searching the knowledge base hasn't answered your question, please contact support.