thank you again for taking care. I have no idea what the difference could be. If I switch back to the automatic mode as described before, I need to set STATIONAP otherwise the module stops working with WIFI on the Airport. This thread seems to cover a similar issue.
So I tried that... result: my existing WLAN network became incredibly slow. Then I run the WLAN sniffer "inSSID Home" to see what's actually going on. Apparently, when running in mode 3, the SoftAP set itself to the same WLAN channel as the station, which was already connected to my existing WLAN network. Regardless of what was specified in the CWSAP command, but also without an returning an ERROR! A CWSAP? confirmed it.
I've also changed the channel of my WLAN from e.g. 3 to 8 and the ESP followed right away. Apparently, the SoftAP has to stick to the channel which is being used by the station and can’t go anywhere else.
Maybe this is the way it has to be due to the architecture of the ESP8266. But running mode 3 just because this will (or might…) keep the station alive is probably not such a great idea after all.
One more thing which puzzled me. How to make the station use its “own” AP? CWLAP never showed the ESP-AP when it was activated – though other WLAN-clients did - and thus, any attempts with CWJAP failed.
I guess I'll put my ESPs back in the drawer for some more time...
ESP8266 only have one hardware channel, eventhrough it could in sta+ap mode.
So it makes ESP8266 station and ap has to be in the same channel.
And ESP8266 station can not use its own softAP, but it can use softAP of another ESP8266.