Mir Welcome to the community!
As a first step, we have checked your line and found that the signal values are very poor. We have created a technician order for this. You will be contacted within 24 hours to arrange an appointment. Please get back to us with feedback after the technician visit.
Regarding your Devolo issue, I recommend the following procedure:
1. disable both WIFI’s on the Sunrise modem (2.4GHz and 5GHz).
2. set your Devolos as an access point and create a WIFI network with its own name.
3. now test your WIFI.
Since you have not deactivated the WIFI of the Sunrise modem, your devices sometimes log into the Sunrise WIFI and sometimes into the Devolo WIFI. This can lead to interruptions or bad performance.
Greetings
Daniele