Juist to give a short update about my case. Having no other idea I have created a new image in a different micro sd card, and - wonder ! - now I could Connect to it from the Stellarmate app on my IPad pro. Still no luck with taking images via the app, because it sets the exposure always to 1s in the sequence, doesn’t matter what I entered when creating the sequence. Waiting for bug fixes.
If you could shed light on the exposure entry trouble I mentioned above, I would be ready to start imaging via the Stellarmate app