Weird Wifi Bug

There’s no bug here; lots of people use networks with hidden SSIDs. Although, to be honest, hiding the SSID has no actual benefit because any Wi-Fi sniffer can find the network anyway; all hiding it does is give a false sense of security.

If the router does not broadcast SSID of course your phone can’t find it; you must set it up manually, entering the SSID into the Wi-Fi settings on the phone. Go to Settings/Wi-Fi/Other, enter the network name and password.

This has nothing to do with the band or the channel. You are better off letting the router chose the channel, rather than assigning a channel manually; it will find the least congested channel on its own.

From→Recommended settings for Wi-Fi routers and access points - Apple Support:

Hidden network

 Set to Disabled

A router can be configured to hide its network name (SSID). Your router might incorrectly use “closed” to mean hidden, and “broadcast” to mean not hidden.

Hiding the network name doesn't conceal the network from detection or secure it against unauthorized access. And because of the way that devices search for and connect to Wi-Fi networks, using a hidden network might expose information that can be used to identify you and the hidden networks you use, such as your home network. When connected to a hidden network, your device might show a privacy warning because of this privacy risk.

To secure access to your network, use the appropriate security setting instead.

And you didn’t read my answer, either. It should work to connect to the hidden network, it does for lots of people (me included), so if it doesn’t work for you then you need to troubleshoot the problem with your phone.