Problem solved!
I knew that Handshake with Thingspeak was part of my problem but I could not find how to.
Now I finally found the Thingspeak library that I did not know. I have been running a ESP8266 for several years knowing that I had fall-outs - but no cure.
Now using the library I get the handshake => problem solved.
Sorry for this noise - this topic can be closed.
Cheers