Occasionally during gameplay I'll notice that I get more and more "shoot the castle" nagging from the game, over and over, repeated one right after another. Eventually there will be a repeated clicking sound in the game somewhere. It's hard to make it happen and it's hard to hear where the sound is emanating from but if I had to guess I would be under the playfield near the top. Nothing seems stuck and there doesn't appear to be any action from the game needed. In fact, when being told to shoot the castle I don't even know if every time the castle was lit up. When this first happened to me the repeated statements and the clicking went on for a good 30-60 seconds.
You can hear it happen right at the beginning of this video. You'll hear "shoot the castle", "shoot the castle" ... "click click click", etc.
The only thing I've seen on the switch tests as an issue right now is the right castle door switch is too sensitive so I get a lot of "oh we oh" Rescue mode happening when I am not in the upper playfield. I don't know if this is related but I'm going to fix that switch soon so I can see if that solves anything. Like I said it's impossible to repeat the issue, as far as I know, as it just happens occasionally.