The ideal network involves your Internet Service Provider (ISP) connecting onsite to a stand-alone modem that connects to a router. If you have more devices on your network than ports on your router, then you can connect a switch to your router to expand the number of ports. If you use an additional router instead of a switch, you will be creating a Double NAT.
This makes it difficult for the messages to make it to and from their destination. There is no fix for a Double NAT other than replacing one of the routers with a switch.
Most issues involving Double NAT will be intermittent meaning it will work one minute then have issues the next. The reason is that the messages don’t always fail to get to and from their destination. Normally the more traffic a user has on their network the more likely they are to experience issues.