What is your issue? I'm in Canada but this feature seems to work pretty well for me - the only thing that's a bit dodgy maybe is that it'll sometimes pick up offramp speed limits when I'm not using the offramp, but otherwise it's a great feature.
Nonetheless, (I'm not an automotive systems software engineer but) I don't think that a Media Control Unit update would affect a feature like this. Please correct me if I'm wrong.
Ah, I see in another thread that you mentioned you're not seeing speed signs at all in your dash/HUD.
Are you using CarPlay or Android Auto? When you are using maps in CarPlay it doesn't show signs, which I suspect is by design as it would be redundant with the speed limits that CarPlay already shows. Still, I dislike this limitation, I wish it still showed signs all the time regardless of whether you're using CarPlay. This probably is an MCU feature that could be affected by a firmware update.