I'm still trying to understand which part of this issue might be a bug and which part is due to system configuration.
When starting the system with a guest account in Ubuntu 16.04.5 LTS, I get the following message when I try to log in into any available wifi networks: "Failed to add/activate connection (7) The access point/org/freedesktop/NetworkManager/AccessPoint/$NUM was not in the scan list."
All connections that are previously saved in my user account does not automatically connect (which is good and I want to keep this way). I understand that this part is easily done in the Network menu by leaving the All users may connect to this network option unchecked.
But I cannot add any new connections while in the guest-user account (which I don't understand why it happens).
If I start the system with a user account, connect to any wifi network and then change to the guest account, I have access to the internet. In that guest session, if I try to connect with any other wifi network, I get the message "Failed to add/activate connection (1) Private connection already active on the device: uid 996 has no permission to perform this operation".
If I then switch back to the user account, the options to disable the wifi or the network appear as grey and I'm not allowed to disable them. That happens also if I terminate the guest session.
Besides discussing this issue, I have one question: - Is it possible to enable the guest account to connect to new wifi networks?
I believe it is fine for the guest session to have access to the internet once the user session activated it, but I don't think it should be unable to create new connections if starting the system with the guest session. Also, I find it strange that the guest session then changes the ability for the user session to change/disable the connection.