(PS4 Slim) I just had my horn vanish soon after starting on Sand Patch service Q276 (AC4400CW) last night. "Horn on" still showed on screen when I pressed L3, but no sound. Never happened before, so I didn't think anything of it, but if it's happening to others also....
This happens to me semi-frequently on Sand Patch. I have found that upon activating the horn, it gets "stuck" in that location for the rest of the session. You can test it by going to the rear free camera view, where you will still be able to hear the horn continuously sounding in the location where you activated it, even after the train is gone. This has only ever happened to me using the AC4400 in SPG (don't have Cane Creek).