Compromised Network, potential man-in-the-middle attack

Hi everyone,

Twice now, within 24h, my wife has had a Norton pop-up on her computer warning of a Compromised Network. The pop-up lists the router, and states "Your personal data and communication may be exposed to an attacker on this network. This type of man-in-the-middle attack aims to downgrade this network's encryption." This is a private network.

The weird thing is that we only get the pop-up on her computer. I haven't received any warnings on mine, even after running a Smart Scan. We are staying in a short-term rental apartment, so the router isn't ours - I don't want to mess too much with it. The landlord had both the router and the internet provider changed yesterday (due to technical problems). The Norton warning only started appearing after the router was changed. The previous router connected to the provider through a coaxial cable. This router uses the mobile network (it has a sim card). It's also a Huawei router - I don't know if that's relevant at all. We both run Win10 computers, and Android phones (which also run Norton, and have not given any alerts).

I have two questions I'm hoping I could get help with:

1. What is the chance that this is a false positive? Should I be worried? Is there any way to test this?

2. What security steps can I take? I was reading a common suggestion is to change the router and wifi login credentials. I suppose I could ask the landlord for permission to do this. However, the router was just installed, and the default password is a random string of letters and numbers so I'm doubtful the password has been compromised... Is there anything else I can do?

Any help or advice would be appreciated!

P.S. This is my first time posting here, so I apologize if I've done something incorrectly.