Hi @Niooi.
Welcome, thank you for reaching out to Sonos Community since you already tried some troubleshooting steps let me try to assist you.
Lets start with the basic one, here are router settings that need to be verified. You can contact your ISP or the manufacturer of the router for assistance.
a. Auto channel must be set to Off
b. Choose best non-overlapping channel (1,6,11)
c. Set channel bandwidth to 20MHz
d. Both 2.4GHz and 5GHz should be enabled
e. 802.11 band should be set to b/g/n
f. Airtime Fairness should be disabled
I’d also be tempted to do a network refresh, by unplugging all Sonos devices, then rebooting the router. When the router comes back up, plug back in the Sonos devices.
Let us know if it works. If you need help with any other information, please be sure to let us know.