Just like the title suggests. There is a question which is most likely deleted (I can't really check, but guessed as much) which still gets displayed (but with a blue background):
When I try to open that question I'm presented with
ERROR: invalid question CONTEXT: PL/pgSQL function _error(integer,text) line 1 at RAISE SQL function "login_question" statement 3 SQL function "login_question" statement 1
I think this shouldn't happen. Either this question shouldn't be displayed to me, or it shouldn't be clickable.
This is an interesting edge case we hadn't thought of, and we will try and fix it.
It looks like you refreshed (or arrived at the page) between @JouleV's flag and mine, quarter of an hour later. In that period you can see the question and it is correctly in your list and shaded to indicate that it is flagged and invisible to unregistered users — that's to draw your attention to it in case it needs more flags or some other kind of help.
After I flagged, the question because invisible to you, so visiting causes that error message (which could be prettier of course).
The bug here is that after I flagged, the question didn't automatically disappear from your list, the way an edit would bump it up to the top.
We will either come up with some way of doing that as part of the normal polling (though it's a bit tricky!), or we'll make a nice error page that includes text along the lines of "the question may have been crew-flagged before you clicked on the link"