Im having trouble setting up Circle since switching over to NBM and different router.
Circle support suggest temporarily disabling 5GHz channel.
Hi - yes, this possible but should not be necessary. The F@ST 5366TN-A Home screen has a 2.4Ghz and a 5GHz tile - select the gear icon of the 5Ghz tile and you can Enable/Disable it there. The two bands should not be interfering with each other.
Have you successfully connected to the Circle Wi-Fi Hot Spot before second stage of install - can you see it broadcasting its ID e.g. Circle_44AE and connected your phone to that network first, then followed the screens which ask you to connect to your modem's Wi-Fi so that you can complete registration, authentication and then user profiles - is this where it is failing to connect - are you selecting the 2.4Ghz or 5 Ghz Modem Wi-Fi at this stage? I don't know if it would any difference - try 2.4Ghz first.
This guy had trouble setting it up on his guest network but overcame problems by asking his children to temporarily disconnect themselves from the modem so that he could complete the install. https://www.youtube.com/watch?v=OXfV97MbJiA
There seems to be two versions of the Circle - Circle 1st Gen has a USB Micro for power, a 10/100 Ethernet port the newer version Circle Home Plus has a USB-C power port and a Built in Battery. The second one seems easier to connect to after all procedures are completed and is suppose to handle 2.4 Ghz and 5 Ghz devices, only after initialisation using the 2.4Ghz Wi-Fi modem network.
Looks like with both versions, after you link to the Circle Wi-Fi 2.4Ghz HotSpot, you then have to use the App to link Modems's 2.4 Ghz Wi-Fi to your Circle. The second connection links the Circle to the modem therefore it has to be onto the modem's 2.4Ghz network.
After completion and registration, it appears that you can then use the Ethernet cable to link the Circle to the Modem, but not before i.e. during the install stage, and later if you have the Circle Home Plus, other devices can be controlled and monitored by the Circle - both 2.4Ghz and 5 Ghz connected devices. It's not clear in the user guide, if you have the 1st Gen. model if all devices need to be on the 2.4Ghz SSID.