The oare the router specs
It has a "backup" 4g WiFi when the WiFi 6 drops. I think that is the LTE component. Could that be the issue?
Specifications
WiFi:
- WiFi 6 (802.11ax)
- 2.5GHz – 4x4 Antenna
- 5GHz – 4x4 Antenna
Memory:
- 1GB Storage Memory
- 1GB Flash Memory
LTE:
LTE Speed:
WiFi Certified:
Check that the 2.4Ghz WiFi network band is 802.11b/g/n compatible as stated in the Sonos specifications and for now, I would set its security mode to ‘WPA2 personal’
To help cut down on interference too, you could also optionally set its channel-width to 20Mhz only. See if that then sorts your issue.
The LTE (mobile) connection you mention is a fallback WAN connection for those ‘hopefully’ rare occasions when your ISP is offline - that should not affect the problem you’re seeing currently with setup and is only ever relevant if your ISP connection is offline anyway.