There is a similar question here already: The StackExchange™ MultiCollider SuperDropdown™ says I've got replies, but I've already viewed those
The issue there was that the OP had viewed the relevant comments / answers / pings, etc., but not the global inbox. My issue is that I have viewed the inbox and (from the inbox) the items that I was being notified of, yet they show up as unread again at some future point.
When I turn on my computer in the morning and log into Stack Exchange, I see that I have one or more unread items in my global inbox, so I click on the global inbox and then, from there, click each notification, opening each item in a new browser tab. When I'm done looking at the new items, I close those tabs and resume my normal browsing on SE and other sites. My inbox at this point shows no unread items.
A few hours later, my global inbox shows new unread items, except when I click on the global inbox, they are the same items I viewed several hours previous. This has happened with pings in chat, new comments, and new answers on questions I've asked.
Specifically, I've had two instances where I had 2 unread items in my inbox: 1 chat message and 1 new comment on an answer. Each instance was a different chat message and a different comment, but in each instance, the notifications for that pair of messages appeared in my inbox as unread, twice, a few hours apart.
I've encountered this problem several times in the last week or so, on multiple browsers (Safari and Chrome) on multiple devices.
Why does the global inbox keep notifying me of messages I've already viewed in the inbox? Is it some sort of caching problem, or is it a bug in the way global inbox notifications work?