Solocam S340: cannot connect to Asus RT-AC86U router

I am not able to connect a Solocam S340 with my Asus RT-AC86U via WLAN/WIFI.
The Asus router runs in Access Point(AP) mode.

The cam connects successfully with a mobile hotspot and with a Fritbox router.
I updated the firmware of the cam successfully to latest version 3.1.7.2.

I tried the following things with the Asus router so far without success:

  • Disabled 5 Ghz
  • Disabled Smart Connect
  • Tried new guest network (only 2.4 Ghz)
  • Setting “Enable WMM No-Acknowledgement” enabled
  • WWM is already enabled
  • MacId of the cam is added to the router, tried also without mac filtering
  • network name and password without any special chars

Thanks for any help