Something very weird is up here. I can't speak to what the behavior would have been before the latest cumulative update because, unfortunately, all of my machines have updated (I think, I'll check my one laptop in a bit).
Those buttons are not recognized as even existing in browse mode and you get "No next button" announced when using the 'b' shortcut for buttons. However, if you bring up the list of elements both are shown. When I activate the member login button via the elements list I am presented with a notification with regard to the site using cookies that is not announced by NVDA.
Now, what's even weirder, is that after reloading the page after that cookies notification, which a screen reader user would not know about, is presented and which makes it disappear, the 'b' command in browse mode works exactly as expected. Still, when I activate the Member Login button I still get the "silent cookies notification" which effectively stops you dead in your tracks unless you interact with it. If I click on the "Agree" for cookies then the member login pop-up dialog appears and NVDA begins interacting with it.
This is all under Chrome. The site is being really cranky about even loading for me under Firefox, and those buttons never even appear. It's doing just fine under Chrome and Edge, so I can't explain that.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
A little kindness from person to person is better than a vast love for all humankind.
~ Richard Dehmel