In conversations on Facebook Messenger (messenger.com), the sender of each message is indicated with an h5. In very simplified code, it goes something like this:
Those h5s are not visually shown; I guess they use thumbnails or some other way of indicating the sender. Instead of being off-screen, they use opacity: 0. That means we now expose them as invisible.
NVDA ignores the invisible state, so thankfully, they still get rendered in NVDA browse mode. I'm not sure about other AT. If we're filtering invisibles out for VoiceOver, this is going to cause a problem there.
Even when the invisible state is ignored, this causes a problem. We return early in GroupPosition if the invisible state is present. That means NVDA can't get the heading level, so it just gets reported as "heading" instead of "heading level 5" and you can't quick nav to heading level 5.