1. I cannot possibly test out "all situations" with regard to Groups.io subscriptions because they vary by individual user. I am subscribed to a total of ten groups, including subgroups, so for single group subscribers it sounds like something is different.
2. It has been mentioned, on I don't know how many topics in this group and others, that when dealing with web browsers (and other apps/applications) that it's always "safest" to be certain you have your screen maximized first. I actually do that myself because it's just too darned easy to switch windows via point and click with the mouse if you're at the edge of one window that's just ever so slightly less than maximized and you hit the pixels for the window beneath that are just peeking out from the edge. I had presumed that "make sure you're maximized" when working on a PC was pretty much standard operating procedure. I will say I've made it standard operating procedure for my students because of what I've learned from this and other screen reader related groups.
I hope that Timothy's additions may have resolved the issues with screen maximization at a minimum and with finding the "Advanced Preferences" link.
I will be happy to try to replicate what happens for any individual who asks me to do so, but that may require your trusting me to access your account strictly for the purposes of testing. I can't delete my groups to make "my world look like yours" but I'm more than willing to take a look at your world strictly for the sake of helping out as far as Groups.io goes. If that were to occur I would ask that you change your password before involving me and changing it again after our work is complete.
I also haven't played with any of the screen readers in "tandem mode" so that would be an option, too. But I'd expect it to be messy, at least from my end, since I'd be a complete newbie with that feature.
Brian - Windows 10 Home, 64-Bit, Version 1703, Build 15063.413
Like all weak men he laid an exaggerated stress on not changing one's mind.