I'm thinking that logging into one will log me out of the other?
That would make sense. You don't want two users messing around with sttings at the same time. (Arlo kicks you out if you sneak up from a different direction.) My experience is that log in with a browser on a PC and the mobile app just won't let you in. You just get some inscrutable "cannot access" response.
Bit it a mess. Needs fixing.
Try it yourself and see what happens. Then maybe we can provoke some action from Netgear.
Re: Logged in from another device, being disconnected
I have tried it, and quite a LOT while doing my 100 hours of troubleshooting over the last two weeks, simply because I thought the two were compatible. It may have been why I was being logged out on some occasions but I truly believe that someone else did somehow gain access. There is just no reason why coincidence would be the answer to my original issue of clicking on the link and then having the issue "pop up" thereafter. I just don't know how these people gain access like this, or why.
So, yes, I have been looking at the log in great detail and noticed succinctly that when I logged into my phone app this morning, I was logged out of the router login. Since I had not logged into my phone the whole morning until then and stayed logged in, it is likely, but I'm a little hyper-aware and unsure of it all since I believe someone else did have access.
