If I search for in:inbox, it also won't show. If I search for both in:inbox is:unread then it does show. If I search for in:spam is:unread it no longer shows, or in: [anythingelsehere] basically. What I'm trying to say is, it CLEARLY is in the inbox, and not somewhere else, but for whatever reason the only way I can find the message is to search specifically with that combo of filter, or to directly search the string of the subject. I can also see it if I just navigate down to "All Mail"
And for the record:
No, I have no filters that should be filtering this email out
No, other messages don't seem to be encountering the issue, just one in particular
No, there are no labels applied to it, unless you count "inbox" as a label (but it won't show if I search label:inbox)
No, it does not show up in any other left hand filter other than "All mail"
No, I don't have any of the weird "primary" and "social" tabs enabled
No, I am not using POP or any other 3rd party tool to interface, this is using latest version of Chrome and going to gmail.com.