HTA 811 with Opener

I have a problem with my Nuki Opener in combination with a Siedle HTA 811.

I live in a House with several Apartments.

When I ring the Bell downstairs the Opener doesn’t recognize the bell in 80% of the time.

Exept this malfunction everything works fine.
I can use all functions of the Siedle HTA 811 (door Opener, speak functions). With the App I can open the door, too.
I also have a Bell directly in Front of my Apartment door where the Siedle HTA 811 gives a different Sound.

When I remove the cable from the luster terminal the Bell doesn’t ring.

Nuki Support has sent me another Opener but same problem. They also told me the wiring was correct.

Now I’m a little bit lost. Can someone tell me how i can improve the Opener so that it will open the door all the time?