My "Access Control" also disappeared

What NG product router model do you have? 

Anytime Access Control is not seen on a routers web page, means that the NH app and Smart Parental Controls which is maintained and used at the NH app level. Thus gets removed from a routers web page. 

If you don't wish to use the NH app or SPC, then you can factory reset the router and setup from scratch using and PC and web browser and then after that completes, Access Controls should be seen on the routers web page: https://kb.netgear.com/22697/How-do-I-install-my-NETGEAR-router-using-the-router-web-interface

I delete the device. This has always solved the problem. Why has access control disappeared?

Management of devices connected to a customer router has nothing to do with the Internet Service Provider.

For decades, Netgear routers (Nighthawk and then Orbi) had a function called Access Control which allowed the user to control which devices were allowed to make use of the network.  (They cannot stop devices from connecting to the network, but can block them from actually using the network.)

When the Smart Parental Controls feature was introduced, Netgear moved the Access Control function from the router to the smartphone app (Nighthawk or Orbi).  This provides additional capabilities, such as setting time parameters.  So, it is a user choice:

• Enable Smart Parental Controls and use the smartphone app to determine access, or
• Not enable Smart Parental Controls and use the web interface Access Control function to determine access.

Once Smart Parental Controls have been enabled, the only practical way to return to the web interface is to perform a Factory Reset and be careful not to enable Smart Parental Controls when configuring the system.

Please check the smartphone app to see if Parental Controls is enabled.