The bell in the living rooms skips a beat every 4 to 6 beats I more likely think that it hits the gong so because how fast the pulse is it might miss the gong
I think the timing for each bell is different. The bell in your room is perfect. The bell in the living room could use an extra MS or so and the Edwards one could loose a MS or two (it had some double dings)
How did you download the panel code during the video or was that an edit. I didn't see you attach anything to the panel to indicate it was getting a download from your computer etc
Couldn't you remove the diode from the bell in the living room so it rings every time the others ring and doesn't skip pulses like it's currently doing?