Friedland Type 4 doorbell with Uni

I have been failing to get anywhere with this for two weeks, so some help would be great.

I have a boring Friedland type 4 doorbell. 12V AC coming from the consumer board, loops out through a standard button press (no light) and back to the solenoid that goes ding dong.

First I tried wiring my Uni up as the first diagram. No button press gets detected at all.'But the doorbell rings like normal.

uniDrawingsimple.jpg

Then I tried disconnecting my switch from the bell and the button press gets detected fine (But the door bell isn't ringing, so that won't work) (not pictured)

Then I tried adding a resistor and diode as I've seen recommended and again, no button press is detected.

uniDrawingDiode.jpg

Finally, I got a relay off the internet and wired that up. Now the button press is independent and can be detected. The shelly can turn on and off the relay (which goes buzzzzzzzz) BUT the doorbell rings permanently

uniDrawingRelay.jpg

I'm at a loss on what to try next. I have a single power source at the bell. I don't require the ability to mute the bell but I do need a working doorbell AND to detect button presses (so I can notify the household on HA)

Thanks for the link.

I've set it up as the diagram (diodes pointing at the uni on VCC and input 1, and using 6 (sensor ground) instead of 2 (neutral)). This lets the button press be detected but the bell is super weak sounding and the UNI goes offline if the button is held for too long.

When I tried with 2 as well as 6, the UNI has ended up in a reboot cycle that disconnecting 2 hasn't resolved.

Ok, having posted that, I realised it had factory reset itself.

For reasons unknown it is now working as I wanted it to two weeks ago.

Why does using Pin 6 (sensor ground) instead of 2 (neutral) work better?

What does the diode on VCC/Live do?

If I want to mute the doorbell (now that I have a fancy relay), will replacing the neutral (pin2) on the Uni for ground (pin 6) on the third diagram above be sufficient to get it working?