Keep the problem reports coming, and one way or another this will get fixed eventually.
This is load related. Search, which powers both of those features, is one of the most resource intensive features on the forum. I has it's own separate load sensing trigger that cuts off search when the server is about to become overloaded. The idea is that search will stop working before the entire site shuts down, hopefully preventing a full shutdown from happening.
We had a hardware upgrade over the winter, but apparently I guessed wrong as usage has grown well beyond what I anticipated. I am hoping that by tuning the server settings just right, we can avoid needing another hardware update before next winter. It is not clear if that will actually work. Even though we seem to be getting by nearly all of the time, now and then things spike up and we overload the server.
The bottom line is that if this is an isolated incident, I will leave things the way they are. But if this repeats regularly I will go ahead and perform the hardware upgrade. In the meantime, I keep finding small adjustments to make to the setup that lets it handle the load just a little more gracefully. So I might be able to take care of it that way.