I have a Ubuntu Linux 20.04 laptop with NC client 3.0.3 and two NC accounts, one where I manage the server (NC 19.0.5) and one where it is managed by someone else.
When I am at home (WIFI under the “SFR” French internet provider “box”) I got disconnected everyday (on both the accounts), and I need to remember to manually re-login every time, but when I am at the university office I don’t have this problem, the client remains connected for months.
I don’t know how long is this odd behavior, it became seriously only this year because… well… you know, we are in 2020/2021, you can guess…
Do you have a login screen for the wifi or soemthing like that? Until then the connection is blocked or the DNS is resolved to a different host (login window). This is not usual at home, but perhaps the computer tries to connect to such a wifi before it connects to your home wifi.
Try with a cable and the box to see if it is perhaps related to something in the box or the ISP.