Does the problem SONOS connect to 2.4GHz or 5GHz ? can that device (Sonos) firmware be updated ?
Try lowering modulation scheme to (Upto 9 MCS TurboQAM) and Adjust Channel Bandwidth to only 20MHz
Then try (one at a time)
- Disable Target Wait Time
- Disable [Protected Management Frames]
- Disable [Wi-Fi Agile Multiband]
Trial and Error I am afraid and if the above fail, I am a little stuck also 
In a completely sane world, madness is the only freedom (J.G.Ballard).
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