Wow! After reading a different thread on a similar issue
and trying different stuff mentioned there it finally worked! Unbelievable 
.
So roughly what I did (maybe helps others or myself for the next switch 
):
- on developer page → zwave → remove any node. Klicking the B button of my RS3 several times. It felt like it didn’t do anything, but who knows.
- Plug in Homey with an extension court so that i could hold it in my arm, next to (~15cm) the RS3, while doing the further steps:
- In Homey App: Add device → Homey (not Fibaro) → Zwave → Install. Then 5-time quick click of B Button, further random clicks. → No device found.
- repeat the above using Fibaro device → not found.
- repeat again using Homey → Zwave. 5-time Click, wait, 5-time click, wait almost until timeout, 3-time click → „wait while device is adding“ (or similar). Yupiiie!
- Perform calibration using Homey app, worked fine!
I must say those last 3 clicks almost never happened. In my head I was already retouring the RS3s to Amazon…
Really strange/random/frustrating procedure, I hope I will succeed 2 more times…
